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Preface
Chapter 1: Introductory Remarks
1. References
Chapter 2: General Methods for the Preparation of Enolates
1. 2.1 Enolate Formation by Deprotonation
2. 2.2 Enolate Formation by Conjugate Addition to α,β-Unsaturated Carbonyl Compounds
3. 2.3 Alkali Metal Enolates by Cleavage of Enol Acetates or Silyl Enol Ethers
4. 2.4 Enolates from Ketenes and Organolithium Compounds
5. 2.5 Enolates from α-Halogen-Substituted Carbonyl Compounds by Halogen–Metal Exchange
6. 2.6 Formation of Enolates by Transmetallation
7. 2.7 Enolates by Miscellaneous Methods
8. References
Chapter 3: Structures of Enolates
1. 3.1 Enolates of Alkali and Alkaline Earth Metals
2. 3.2 Enolates of Other Main Group Metals
3. 3.3 Transition Metal Enolates
4. References
Chapter 4: Enolates with Chiral Auxiliaries in Asymmetric Syntheses
1. 4.1 Auxiliary-Based Alkylation of Enolates
2. 4.2 Auxiliary-Based Arylation of Enolates
3. 4.3 Auxiliary-Based Aldol, Vinylogous Aldol, and Reformatsky Reactions
4. 4.4 Auxiliary-Based Mannich Reactions and Ester Enolate-Imine Condensations
5. 4.5 Auxiliary-Based Conjugate Additions
6. 4.6 Auxiliary-Based Oxidation of Enolates
7. References
Chapter 5: Enolates in Asymmetric Catalysis
1. 5.1 Enantioselective Catalysis in Alkylations and Allylations of Enolates
2. 5.2 Enantioselective Catalysis for Enolate Arylation
3. 5.3 Catalytic, Enantioselective Aldol, Vinylogous Aldol, and Reformatsky Reactions
4. 5.4 Catalytic Enantioselective Mannich Reactions, Ester Enolate–Imine Condensations, and Imine Reformatsky Reactions
5. 5.5 Catalytic Enantioselective Conjugate Additions
6. 5.6 Enantioselective Protonation of Enolates
7. 5.7 Enantioselective Oxidation of Enolates
8. References
List of Procedures
Index
End User License Agreement

List of Illustrations

Chapter 1: Introductory Remarks
1. Figure 1.1 Formation of the enolate anion by removal of an α-hydrogen by base is the first step in the aldol addition [2].
2. Scheme 1.1 General enolate structures.
3. Scheme 1.2 Examples of nonequivalency of α-substituents in lithium enolates 4 and 5, rhodium enolate 6, and palladium enolate 7.
4. Scheme 1.3 General structures of diastereomeric cis- and trans-O-bound enolates.
5. Scheme 1.4 Opposite assignment of configurations (Z and E) in an ester enolate depending on the O-bound metal.
6. Scheme 1.5 Examples of contradictory assignment of configurations in enolates.
7. Scheme 1.6 Rhodium and palladium enolates. Equilibrating O- and C-bound tautomers 14 and 15; rhodium complex 16, characterized by its crystal structure, as an example of an η³-oxallyl enolate; cationic palladium complex 17, proven as intermediate in Shibasaki's enantioselective aldol addition.
8. Scheme 1.7 Diastereoselective methylation of 3-hydroxybutanoate 18–an example of a diastereoselective conversion of a lithium enolate with a chiral skeleton.
Chapter 2: General Methods for the Preparation of Enolates
1. Figure 2.1 (a) Top: Structure of LiHMDS (crystallized from pentane). Copied from Ref. [61a]. (b) Bottom: Structure of LDA (crystallized from THF).
2. Scheme 2.1 Standard bases for the formation of alkali metal enolates.
3. Scheme 2.2 Preparation of Rathke's enolate 11.
4. Scheme 2.3 Preparation of Ivanov's reagent 12 and dilithiated carboxylic acids 13.
5. Scheme 2.4 Regioselective preparation of less substituted enolates derived from 2-methylcyclohexanone.
6. Scheme 2.5 Kinetically controlled, regioselective deprotonation of selected ketones.
7. Scheme 2.6 Contrathermodynamic formation of lithium enolates 18a and 18b derived from 2-arylcyclohexanones.
8. Scheme 2.7 Example for formation of the higher-substituted enolate by deprotonation under thermodynamic control; R = CH₂CH₂OSitBuMe₂.
9. Scheme 2.8 Regioselective deprotonation reactions of α,β unsaturated ketones. Compound 25e: cholest-4-en-3-one.
10. Scheme 2.9 Formation of cis-enolates from alkyl–aryl ketones 31 and 34 and N-acyl-pyrroles 37.
11. Scheme 2.10 Enolates derived from α- and β-hetero-substituted carbonyl compounds.
12. Scheme 2.11 Stereochemistry in the formation of ester enolates: Ireland's cyclic model (top) and Heathcock's acyclic model. The latter was originally formulated with HMPA that has been replaced here by DMPU which is known to a similar effect.
13. Scheme 2.12 Stereochemistry in the formation of amide and ketone enolates according to Ireland's model.
14. Scheme 2.13 Dimeric solution structures of LDA with lithium coordinating to donor ligands.
15. Scheme 2.14 Transition-state models for the deprotonation of cyclohexanoic ester 54 with LDA in different solvents and cosolvents.
16. Scheme 2.15 Participation of triethylamine in the deprotonation of ketones with LiHMDS.
17. Scheme 2.16 Rationale for the deprotonation of 4-fluoroacetophenone by LDA, based on rapid-injection ¹⁹F-NMR studies. Solvation of lithium not shown; Ar = 4-FC₆H₄.
18. Scheme 2.17 Mixed aggregates of lithium amide bases and lithium halides.
19. Scheme 2.18 Mechanism of enolate formation starting from a mixed LiBr–LiNH₂ aggregate according to a computational study.
20. Scheme 2.19 Proposed transition-state models for enolate formation starting from heterotrimers of carbonyl compound, lithium amide base, and lithium halide.
21. Scheme 2.20 Enantioselective enolate formation by treatment of 4-t-butylcyclohexanone with C₂-symmetric lithium amide bases (R,R)-72a or (S,S)-72a.
22. Scheme 2.21 Selected chiral lithium amide bases used for enantioselective enolate formation.
23. Scheme 2.22 Enantioselective formation of axially chiral lithium enolate 80.
24. Scheme 2.23 Dimeric structures of chiral lithium amide bases and their mixed aggregates with lithium halides.
25. Scheme 2.24 Regioselective formation of boron enolates according to Mukaiyama's protocols; transition-state model 91 for kinetically controlled enolate generation.
26. Scheme 2.25 Selected cis-configured boron enolates.
27. Scheme 2.26 Controlled generation of cis- and trans-boron enolates from ketones.
28. Scheme 2.27 Controlled generation of cis- and trans-boron enolates from thioesters.
29. Scheme 2.28 Formation of boron enolates derived from carboxylic esters and thioesters.
30. Scheme 2.29 Generation of tin enolates by deprotonation; selected examples of tin enolates 105 used in asymmetric aldol reactions.
31. Scheme 2.30 Generation of titanium enolates by deprotonation; equilibrium of titanate 106 and titanium enolate 107.
32. Scheme 2.31 Formation of zinc enolate 109, embedded in Trost's Bis-Pro-Phenol ligand.
33. Scheme 2.32 General scheme of a conjugate addition as a route to enolates.
34. Scheme 2.33 Enolate formation and quenching in a Birch reduction.
35. Scheme 2.34 Regioselective generation of enolate 112 by reduction and subsequent alkylation.
36. Scheme 2.35 Correlation between enone conformation and enolate configuration.
37. Scheme 2.36 Enolates 122 in consecutive conjugate additions of lithiated thioacetals to butenolide 120 and subsequent and hydroxyalkylation/alkylation.
38. Scheme 2.37 Copper catalyzed generation of magnesium enolate 123 by conjugate addition.
39. Scheme 2.38 Consecutive conjugate addition of vinylcopper reagent 126 and vinylogous addition of enolate 128 in stereoselective prostaglandin synthesis R = SitBuMe₂.
40. Scheme 2.39 Simplified mechanism [135] of enolate formation by conjugate addition of lithium cuprates to α,β-unsaturated carbonyl compounds.
41. Scheme 2.40 Enantioselective conjugate addition catalyzed by bimetallic complex 135 and consecutive aldol addition of aluminum enolate 136.
42. Scheme 2.41 Enantioselective rhodium-catalyzed conjugate addition of a borane and subsequent diastereoselective aldol addition of boron enolate 140.
43. Scheme 2.42 Conjugate addition of chiral lithium amide 142 and under formation of cis-lithium enolates 43b and quenching as silyl ketene acetal (Z)-144.
44. Scheme 2.43 Stereochemical stability of lithium enolates cis-146 and trans-148 generated by cleavage of enol acetates.
45. Scheme 2.44 Formation of lithium enolates by cleavage of silyl enol ethers.
46. Scheme 2.45 Diastereoselective formation of lithium enolates by addition of alkyllithium reagents to ketenes. In situ preparation of ketenes from BHT esters.
47. Scheme 2.46 Formation of lithium, magnesium, and zinc enolates by halogen–metal exchange.
48. Scheme 2.47 Preparation of molybdenum and tungsten enolates 163 through halogen–metal exchange in various α-chloro carbonyl compounds.
49. Scheme 2.48 General scheme for transmetallation of enolates.
50. Scheme 2.49 Controlled preparation of the different metalla tautomers of rhodium enolates: η³-oxallyl tautomer 168, η¹-oxygen-bound enolate 169, and η¹-carbon-bound enolate 170.
51. Scheme 2.50 C-bound nickel and palladium enolates prepared by transmetallation.
52. Scheme 2.51 Formation of titanium enolates 174 by cleavage of silyl enol ethers.
53. Scheme 2.52 O-bound palladium enolate 177 generated in situ from silyl enol ether 176 by transmetallation.
54. Scheme 2.53 In situ formation of palladium enolates 180 and/or 181 in catalytic enolate arylation reactions.
55. Scheme 2.54 Preparation of O-bound palladium ester enolate 184 by transmetallation.
56. Scheme 2.55 Generation of enolates by miscellaneous methods.
57. Scheme 2.56 Ion pair 194 and palladium complex 195 as alternatives of enolates formed in the course of decarboxylative allylic alkylation.
58. Scheme 2.57 Generation of enolates 198 through oxy-Cope rearrangement of alkoxides 197.
Chapter 3: Structures of Enolates
1. Figure 3.1 Crystal structures (illustrative examples) of lithium enolates.
2. Figure 3.2 (a) Structure of dimeric THF-solvated lithium enolate of p-fluorophenyl benzyl ketone. Copied from Ref. [7]. (b) Structure of a cis-configured magnesium enolate of t-butyl ethyl ketone.
3. Figure 3.3 (a) Structure of a mixed aggregate formed from sodium pinacolate and pinacolone and (b) structure of lithium pinacolate–pinacolone aldolate.
4. Figure 3.4 Structure of the monomeric lithium enolate of dibenzyl ketone with the metal complexed by the tridentate PMDTA ligand.
5. Figure 3.5 ¹H-DOSY spectrum of mixed enolate aggregate 4.
6. Figure 3.6 Job plot showing relative integrations of R_nS_6−n hexamers derived from enolates (R)- and (S)-9 as a function of the mole fraction of the (R) enantiomer. The curves correspond to a parametric fit to a hexameric enolate.
7. Figure 3.7 Computed transition structures (HF 6-31+g^*) for the reaction monomeric (top) and dimeric (bottom) lithium enolate of acetaldehyde with methyl chloride.
8. Figure 3.8 The aldol reaction of tetrameric lithium enolate of 4-fluoroacetophenone (10) with 4-fluorobenzaldehyde in 3:2 THF/Et₂O at −125 °C monitored by ¹⁹F rapid injection NMR. The lines correspond to simulations based on the kinetic scheme shown above with the rate constants indicated on the graph.
9. Figure 3.9 B3LYP/6-31 + G(d) optimized geometries of tetra-solvated tetrameric lithium enolates. Hydrogens are omitted for clarity. From (a–d): acetaldehyde enolate, acetone enolate, cyclohexanone enolate, and pinacolone enolate.
10. Figure 3.10 (a) Calculated η³ global minimum of unsolvated lithium enolate of acetaldehyde and (b) calculated O-bound global minimum of lithium enolate of acetone, tri-solvated by dimethyl ether.
11. Figure 3.11 Molecular structure of bis(diisopropylamino)boron enolate of pinacolone (14). Hydrogen atoms are omitted for clarity.
12. Figure 3.12 Palladium(II) enolates: examples of C-bound tautomers 44 and O-bound tautomers 45. Molecular structures of 44 (R¹ = R² = H, R³ = 4-MeC₆H₄, Ar = 2-MeC₆H₄) and 45 (R¹ = Me, R² = H, Ar = Ph).
13. Figure 3.13 Molecular structure of the unligated enolate of ethyl phenylacetate with bis(phenanthroline) complexed Cu(I) cation.
14. Figure 3.14 Molecular structure of the Reformatsky reagent [BrZnCH₂CO₂CMe₃·THF]₂.
15. Scheme 3.1 Preparation and structure of the lithium enolate – LDA aggregate 2. In the drawings within this chapter, no distinction is made between covalent and coordinative bonds.
16. Scheme 3.2 Preparation and structure of a mixed aggregate 4 composed of cis-configured lithium enolate of 3-pentanone and lithiated chiral amino alcohol 3.
17. Scheme 3.3 Preparation methods and structure of lithium enolate–lithium halide aggregates 5.
18. Scheme 3.4 Enolates 6–8, studied by multinuclear NMR titration. Structures of tridentate ligands PMDTA and TMTAN.
19. Scheme 3.5 Dimeric O-bound aluminum enolates 15 and 16, derived from N,N-dimethylglycine ester and aryl methyl ketone, respectively.
20. Scheme 3.6 Calculated relative energies of equilibrating O- and C-bound tautomers of tin enolates derived from acetophenone and methyl acetate.
21. Scheme 3.7 O-metal bound dimeric yttrium enolate 17 and monomeric scandium enolate 18, both derived from acetaldehyde.
22. Scheme 3.8 Selected structures of O-bound titanium and zirconium enolates, confirmed by crystal structure analyses.
23. Scheme 3.9 O-metal-bound enolate 24 and aldolate 25 with hexa-coordinated titanium, both characterized by crystal structure analyses.
24. Scheme 3.10 Typical examples of manganese, molybdenum, and tungsten: C-bound enolates 26 and 27 and η³-oxallyl enolates 28 and 29.
25. Scheme 3.11 O-bound rhenium(I) enolate 30 and iron(II) enolates 31 and 32.
26. Scheme 3.12 Representative examples of different tautomers of rhodium(I) enolates: C-bound enolate 33, O-bound enolates 34, and η³-oxallyl-type enolates 35 and 36.
27. Scheme 3.13 C-bound nickel and palladium enolates 37, O-bound palladium enolate 38a, and equilibrium between O-bound tautomer 38b and C-bound tautomer 39.
28. Scheme 3.14 Representative examples of palladium(II) enolates: O-bound palladium enolates 40 and 42; dimeric C,O-bridged palladium enolates 41 and 43.
29. Scheme 3.15 Chelated zinc enolate 47 and tetramer 48.
30. Scheme 3.16 O-bound zinc enolates with complexation of the metal by diamines.
Chapter 4: Enolates with Chiral Auxiliaries in Asymmetric Syntheses
1. Scheme 4.1 Diastereoselective alkylation of propionate 1 via lithium enolates trans-2 and cis-3.
2. Scheme 4.2 An early auxiliary-based enolate alkylation: preparation of pheromone (S)-10 from N-propionyl (1S,2R)-ephedrine 8.
3. Scheme 4.3 Alkylation of N-propionyl prolinol 11 through lithium and lithium/potassium enolates and cleavage of the auxiliary.
4. Scheme 4.4 Alkylation of C₂-symmetric amides 18.
5. Scheme 4.5 Diastereoselective alkylation reactions of pseudoephedrine-based auxiliaries 21. Cleavage of the auxiliary and model 29 for the stereochemical outcome.
6. Scheme 4.6 Alkylation of glycine through the amide auxiliary 30.
7. Scheme 4.7 Glycine alkylation through camphor-derived auxiliary 35.
8. Scheme 4.8 Diastereoselective alkylations of aminoindanol-derived amides 38 and 40. Applications in syntheses of indinavir and endothelin receptor antagonist 44.
9. Scheme 4.9 Evans auxiliaries 45–47 and examples for alkylation reactions of enolates 49 and 52.
10. Scheme 4.10 Selected examples for the cleavage of Evans auxiliaries from alkylation products 54.
11. Scheme 4.11 “Post-Evans” heterocyclic auxiliaries used after N-acylation for enolate alkylations.
12. Scheme 4.12 Alkylation of oxazolidinone-derived enolates with α-oxy substituents.
13. Scheme 4.13 Application of Evans' auxiliary for a synthesis of alcohol 72, a building block for ionomycin.
14. Scheme 4.14 Alkylation reactions of oxazolidinones 73 and 78 through titanium enolates.
15. Scheme 4.15 Methoxyalkylation of thiazolidinethiones 80 and 80b through titanium enolates. Transition state model 84.
16. Scheme 4.16 Alkylation of thiazolidinethiones (R)- and (S)-80 with glycals via titanium enolates.
17. Scheme 4.17 Application of Evans enolates in large-scale synthesis of PNP405.
18. Scheme 4.18 Application of Oppolzer sultams 91 and ent-91 in enolate alkylations.
19. Scheme 4.19 Iterative alkylations of Meyers' bicyclic lactams 99; model 104 for the approach of alkyl halide to the enolate.
20. Scheme 4.20 Alkylation of the fused δ-lactam 105 and cleavage of the chiral auxiliary.
21. Scheme 4.21 Enolate alkylation in Seebach's self-regeneration of chirality.
22. Scheme 4.22 Alkylation of dioxolanone 115 via the lithium enolate and application in a synthesis of (+)-frontalin.
23. Scheme 4.23 Alkylation reactions of imidazolidinone (S)-118 and application for a synthesis of NMDA-receptor antagonist 123.
24. Scheme 4.24 Alkylation reactions of Davies–Liebeskind enolates 125 and 128.
25. Scheme 4.25 Application of Davies–Liebeskind enolates in a synthesis of (−)-captopril.
26. Scheme 4.26 Arylation of chiral silicon enolates 132 and 134.
27. Scheme 4.27 Palladium-catalyzed arylation and vinylation of dioxolanone 137.
28. Scheme 4.28 General mechanism of aldol reactions with preformed enolates 143.
29. Scheme 4.29 General overview on the stereochemistry of the aldol addition with preformed enolates 143.
30. Scheme 4.30 Stereochemical correlation between enolate and aldol configuration according to Zimmerman–Traxler transition state models 149 and 151.
31. Scheme 4.31 Mulzer's transition state model 153 of the aldol addition.
32. Scheme 4.32 Noyori's open transition state models 156 and 157 of the aldol addition. Independence of syn-aldol configuration from enolate configuration.
33. Scheme 4.33 Open and cyclic transition state models of the Mukaiyama aldol addition.
34. Scheme 4.34 Selection of chiral ketones used as enolates in aldol reactions.
35. Scheme 4.35 Solladié–Mioskowski acetate aldol reaction with chiral sulfoxides 168.
36. Scheme 4.36 Braun–Devant acetate aldol addition of doubly deprotonated triphenylglycol ester (R)-173.
37. Scheme 4.37 Selection of natural products and drugs synthesized through Braun–Devant aldol addition of (R)- and (S)-triphenylglycol acetates 173.
38. Scheme 4.38 Application of the acetate aldol addition of triphenylglycol ester (S)-173 for syntheses of HMG-CoA reductase inhibitors atorvastatin, lovastatin, and fluvastatin.
39. Scheme 4.39 Aldol addition of triphenyl glycol ester 173 to bicyclic ketone 180 as the key step in a synthesis of the selective α7 nicotinic receptor agonist AR-R17779.
40. Scheme 4.40 Acetate aldol reaction of Yamamoto's ester 183.
41. Scheme 4.41 Aldol reactions with Helmchen's and Oppolzers's auxiliaries 1 and 188. Transition state models 192 and 193 for rationalizing the stereochemical outcome.
42. Scheme 4.42 Mukaiyama aldol addition with ephedrine-derived silicon enolate 195.
43. Scheme 4.43 Masamune's aldol addition of ephedrine-derived boron enolate 198.
44. Scheme 4.44 Aldol addition of aminoindanol-derived propionate 200 via the titanium enolate; transition state model 203.
45. Scheme 4.45 Propionate aldol addition via triphenylglycol ester (R)-204.
46. Scheme 4.46 “Evans-syn” selective aldol addition of valine-derived N-propionyl oxazolidinone 48 via boron enolate 208. Dipole-minimized transition state model 210.
47. Scheme 4.47 Evans aldol addition with phenylalanine-derived imide 73 and cleavage of the auxiliary by hydrolysis.
48. Scheme 4.48 Evans aldol reaction of ephedrine-derived N-propionyloxazolidinone 51 and conversion of the adduct 213 into Weinreb amide 214 under cleavage of the auxiliary.
49. Scheme 4.49 Access to “non-Evans-syn” aldol adducts 216 via titanium tetrachloride-mediated aldol addition; proposed transition state model 217 with boron chelation and titanium coordination.
50. Scheme 4.50 Crimmins' stereodivergent aldol additions of oxazolidinethione 218 and thiazolidinethiones 220. Transition state models 222 and 223 as rationale for the formation of “Evans-syn” and “non-Evans-syn” aldol adducts.
51. Scheme 4.51 Anti-selective aldol reactions through magnesium enolates. Transition state models 224 and 227 for the stereodivergent access to diastereomeric anti-aldols 225 and 228, respectively.
52. Scheme 4.52 Aldol additions of N-acyl-oxazolidinones 229 carrying α-hetero substituents.
53. Scheme 4.53 Unselective Evans' N-acetyl oxazolidinone 231 and selected auxiliaries 232, 234, and 237 for acetate aldol additions.
54. Scheme 4.54 Evans' remote asymmetric induction in aldol additions of keto imides 238 via titanium and tin enolates. Transition state models 239 and 241 for rationalizing the stereochemical outcome.
55. Scheme 4.55 Selection of natural products synthesized by using aldol reactions with Evans' chiral auxiliaries. Stereogenic centers generated by these methods are marked by an asterisk.
56. Scheme 4.56 Multiple use of Evans auxiliary-based protocols in a total synthesis of calyculin A.
57. Scheme 4.57 Application of Evans' auxiliary 73 and Seebach's oxazolidinone 247 in the Novartis large-scale synthesis of (+)-discodermolide.
58. Scheme 4.58 Evans aldol protocol as the key step in Novartis' synthesis of ritalin.
59. Scheme 4.59 Kobayashi's vinylogous Mukaiyama aldol reactions of silicon dienolates 252 and 255. Open transition state models 257 and 258 for rationalizing the stereochemical outcome.
60. Scheme 4.60 Vinylogous Mukaiyama aldol addition of silyldienolates 259 and ent-255 as a key step in total syntheses of palmerolide A.
61. Scheme 4.61 Aldol reaction of tethered silicon enolate 263. Pseudorotation of enolate–aldehyde complexes 265 and 266.
62. Scheme 4.62 Stereodivergence in aldol additions of Oppolzer's sultam 92 via boron, tin, and silicon enolates. Proposed transition state models 273–275.
63. Scheme 4.63 Mukaiyama acetate aldol reaction with silyl enol ether 276 derived from Oppolzer's sultam. Proposed open transition state 277.
64. Scheme 4.64 Acetate aldol addition with iron acetyl complex 124b via Davies–Liebeskind enolates.
65. Scheme 4.65 Masamune's aldol reaction mediated by the C₂-symmetric borolane as a chiral controller in enolates 283. Transition state model for the propionate and acetate aldol additions 286 and 287, respectively.
66. Scheme 4.66 Aldol additions of methyl ketones, mediated by chiral borane ligands 282b and 289. Applications in syntheses of ent-gingerol and statin.
67. Scheme 4.67 Diisopinocampheylboranes 292 as controllers in Paterson's aldol procedure. Application in a total synthesis of swinholide A.
68. Scheme 4.68 Corey's syn- and anti-selective aldol protocols based on the C₂-symmetric diazaborolidines. Transition state models 308 and 309 for rationalizing the correlation between enolate and aldol configurations.
69. Scheme 4.69 Application of oxazaborolidine 300 for mediating anti-selective aldol additions of bromoacetate 310.
70. Scheme 4.70 Acetate aldol additions mediated via titanium enolates with chiral ligands derived from diacetone glucose and TADDOL 312 and 313, respectively.
71. Scheme 4.71 Aldol additions of N-protected glycinates 318 mediated via chiral titanium enolates 319 and 321.
72. Scheme 4.72 α-Bromo N-acyloxazolidinones 323 and 326–328 as auxiliaries for asymmetric Reformatsky reactions.
73. Scheme 4.73 Influence of imine protecting group on the stereodivergent titanium tetrachloride-mediated Mannich reactions of thiazolidinethione 80a.
74. Scheme 4.74 Application of the Mannich reaction of N-acyl oxazolidinone 335 in a synthesis of the β-lactam ezetimibe.
75. Scheme 4.75 Mukaiyama–Mannich reactions with galactosamine-derived imines 338.
76. Scheme 4.76 Domino Mannich–Micheal sequence in Kunz' synthesis of (S)-coniine.
77. Scheme 4.77 Mannich reactions of glycinates and sulfinylimine (S)-348. Transition state models 355 and 357 for the reactions of trans-enolate 354 and cis-356, respectively.
78. Scheme 4.78 Ojima's condensation of imines with esters 358 and 364 derived from menthol and phenylcyclohexanol. Application in a synthesis of the phenylisoserine side chain of Taxol.
79. Scheme 4.79 Trans- and cis-β-lactams 367 and 368, respectively, by condensation of triphenylglycol-derived esters 204 and 205 with imine 359a.
80. Scheme 4.80 Synthesis of the cholesterol absorption inhibitor SCH48461 by ester enolate-imine condensation.
81. Scheme 4.81 Mannich reactions mediated by Corey's diazaborolidine. Transition state model 374 and conversion of β-amino thioesters 375 into β-lactams 376.
82. Scheme 4.82 Rhodium catalyzed difluoro imine Reformatsky reaction of menthyl ester 378 for the synthesis of difluoro β-lactams 379.
83. Scheme 4.83 Large-scale application of a Reformatsky–Mannich reaction in a synthesis of the α_vβ₃-integrin antagonist 386.
84. Scheme 4.84 Selection of chiral auxiliaries used in acceptors for conjugate additions.
85. Scheme 4.85 Conjugate additions to enoyl sultams 391. Models 392 and 394 for rationalizing the dichotomy of the reactions in the absence and presence of cuprous chloride.
86. Scheme 4.86 Application of the conjugate addition of aryllithium compound 398 to the chiral acceptor 397 in a synthesis of endothelin A receptor antagonist 400.
87. Scheme 4.87 Regioselective and diastereoselective formation of enolate 403 by conjugate addition to dienoyl sultam 401 and subsequent aldol addition of the enolate.
88. Scheme 4.88 Formation of lithium enolate 407 by conjugate addition of lithiated hydrazine 406 and subsequent diastereoselective alkylation.
89. Scheme 4.89 Conjugate additions of the chiral lithium amide 409 to α,β-unsaturated esters and amides and subsequent alkylation.
90. Scheme 4.90 Conjugate addition of the chiral lithium amide 409 as a key step in Merck's synthesis of the α_vβ₃ integrin antagonist 420.
91. Scheme 4.91 General stereochemical scheme of the Michael addition.
92. Scheme 4.92 Corey's procedure for Michael additions of phenylmenthyl ester 424. Influence of the configuration of the Michael acceptor on the stereochemical outcome and its rationalization by transition state model 428.
93. Scheme 4.93 Transition state model for Michael additions of lithium enolates 430 and 431 with opposite configurations.
94. Scheme 4.94 Selected chiral enolates as donors for Michael additions.
95. Scheme 4.95 Conjugate additions of Evans' oxazolidinones to acrylonitrile and nitroalkene 442 via titanium enolates.
96. Scheme 4.96 Stereodivergent course in Davis' hydroxylation of amide 445, depending on the enolate metal. Models 446 and 449 as a rationale for the stereochemical dichotomy.
97. Scheme 4.97 Evans' hydroxylation of N-acyl oxazolidinones 452, 454, 456, and 458 via the sodium enolates.
98. Scheme 4.98 Oxidation of N-acyl oxazolidinones 459 with TEMPO via the titanium enolates.
99. Scheme 4.99 Brigaud's enolate oxidation with molecular oxygen. Hydroxylation of N-acyl oxazilidines 464, cleavage of the auxiliary, and transition state model 467.
100. Scheme 4.100 Evans' azidation of N-acyl oxazolidinones 468 and 474 via the potassium enolates. Cleavage of the auxiliary and application of enolate amination for a synthesis of tripeptide OF-4949-III (476).
101. Scheme 4.101 Amination of N-acyl oxazolidinones 468 by reaction of the lithium enolates with azodicarboxylate.
102. Scheme 4.102 Stereodivergent reactions of potassium versus lithium enolates of N-acyl pyrazolidinones 481 and reductive cleavage of the auxiliary.
103. Scheme 4.103 Amination of Oppolzer sultams 92 by reaction of the potassium enolates with nitroso compound 486. Cleavage of the auxiliary and model 491 as a rationale of the stereochemical outcome.
104. Scheme 4.104 Bromination of Evans' boron enolates 493 with NBS and replacement of the halogen by azide. Halogenation of silyl ketene acetals 497 with NCS and NBS.
105. Scheme 4.105 Electrophilic fluorination of N-acyl oxazolidines 464 via the sodium enolate by reaction with N-fluorobenzenesulfonimide. Cleavage of the auxiliary and transition state model 501.
106. Scheme 4.106 Homodimerization of N-acyl oxazolidinones 468 by reaction of the lithium enolate with titanium tetrachloride.
107. Scheme 4.107 Baran's hetero dimerization of imide and ketone enolates 507 and 504. Proposed mechanism and transition state models 514 and 515.
108. Scheme 4.108 Application of Barans's enolate heterodimerization in a synthesis of (−)-bursehernin.
Chapter 5: Enolates in Asymmetric Catalysis
1. Figure 5.1 Calculated transition state for the allylic alkylation of the lithium enolate of (R)-γ-valerolactone 49a mediated by (S)-BINAP. Visualization of the outer-sphere mechanism.
2. Figure 5.2 Transition state model of Mukaiyama's aldol addition, mediated by the tin(II) complex of ligand 176a.
3. Scheme 5.1 Examples of Koga's tetradentate ligands 1 and formation of aggregates 2 by deprotonation of a carbonyl compound.
4. Scheme 5.2 Examples of enantioselective alkylation after formation of enolates by means of chiral lithium amide 1a.
5. Scheme 5.3 Catalytic use of chiral lithium amide 2b in enantioselective benzylation of α-tetralone.
6. Scheme 5.4 Enantioselective alkylation of tin enolates, catalyzed by chromium salen complex 5.
7. Scheme 5.5 Enantioselective alkylation of cis/trans-mixtures of tin enolates 6, catalyzed by chromium salen complex 7.
8. Scheme 5.6 Simplified catalytic cycle of the palladium-catalyzed allylation of preformed enolates. MX and MX′ may be not identical in cases where the anion undergoes conversion, for example, decarboxylation in the case of a leaving group ROCO₂⁻.
9. Scheme 5.7 Trost's asymmetric allylic allylation of 2-methyl-1-tetralone through the tin enolate 13a.
10. Scheme 5.8 Enantioselective allylic alkylation as a key step in a synthesis of hamigeran B.
11. Scheme 5.9 Diastereoselective and/or enantioselective palladium-catalyzed allylic alkylation of cyclohexanone through the magnesium or lithium enolate.
12. Scheme 5.10 Regioselective, diastereoselective, and enantioselective palladium-catalyzed allylic alkylation of acyclic ketones 25 through their lithium enolates.
13. Scheme 5.11 Regioselective, diastereoselective, and enantioselective palladium-catalyzed allylic alkylation of acylsilanes through their lithium enolates.
14. Scheme 5.12 Enantioselective palladium-catalyzed allylic alkylation of tertiary amides 32 through their lithium enolates.
15. Scheme 5.13 Rhodium-catalyzed enantioselective allylation of lithium enolates derived from α-oxy-substituted ketones 36.
16. Scheme 5.14 Diastereoselective and enantioselective allylic alkylation of glycinate-derived chelated zinc enolate 41.
17. Scheme 5.15 Diastereoselective and/or enantioselective palladium-catalyzed allylation of δ-valerolactone through the lithium enolate 46.
18. Scheme 5.16 Cooperative and antagonistic effects of reagent and substrate stereocontrol in allylic alkylations of (R)-lactones 49.
19. Scheme 5.17 Reagent control in the highly diastereoselective allylic alkylation of δ-caprolactone (R)-49b through the lithium enolate.
20. Scheme 5.18 Palladium-catalyzed allylic alkylations of doubly deprotonated carboxylic acids.
21. Scheme 5.19 Diastereoselective and enantioselective allylation of doubly deprotonated phenylacetic acid.
22. Scheme 5.20 Stereochemical course of the palladium-catalyzed allylic substitution. Inner- and outer-sphere mechanisms.
23. Scheme 5.21 Stereochemical course of the palladium-catalyzed allylic substitution at the substrate (Z)-60 as a diastereomerically and enantiomerically pure probe.
24. Scheme 5.22 Complementary stereochemical course of the palladium-catalyzed allylic substitution at the substrate (E)-65 as diastereomerically and enantiomerically pure probe.
25. Scheme 5.23 Stereochemical course in the palladium-catalyzed reaction of lithium enolate with the probe rac-68, mediated by the chiral ligand (R,R)-69.
26. Scheme 5.24 Enantioselective palladium-catalyzed allylic alkylation of silyl enol ethers 74 and 76 in the presence of t-butyl-PHOX ligand 42b and the activator Bu₄NPh₃SiF₂.
27. Scheme 5.25 Catalytic cycle of the palladium-catalyzed allylic alkylation of silyl enol ethers under activation by fluoride and/or alkoxide.
28. Scheme 5.26 Enantioselective palladium-catalyzed allylic alkylation of fluoro-substituted silyl enol ethers 80.
29. Scheme 5.27 Regioselective and enantioselective iridium-catalyzed allylic alkylation of silyl enol ethers 82.
30. Scheme 5.28 Kinetic resolution in the reaction of racemic allylic acetate 86 with 2-trimethylsiloxyfuran, mediated by palladium with the chiral ligand (R,R)-14.
31. Scheme 5.29 Enantioselective palladium-catalyzed allylic alkylation of silyl ketene acetals 88 without external activation.
32. Scheme 5.30 Mechanistic pathways in the palladium-catalyzed decarboxylative allylic alkylation, starting from allyl β-keto esters 91 or allyl enol carbonates 92.
33. Scheme 5.31 Enantioselective decarboxylative allylic alkylation of β-keto esters 99, reported by Tunge.
34. Scheme 5.32 Enantioselective decarboxylative allylic alkylations, starting from allyl enol carbonates 101 (reported by Stoltz) and allyl enol carbonates 103 (reported by Trost).
35. Scheme 5.33 Influence of the configuration at the enol double bond on the stereochemical outcome of the decarboxylative allylic alkylation, mediated by ligand (R,R)-69.
36. Scheme 5.34 Diastereoselective and enantioselective formation of diketone (R,R)-108 by decarboxylative allylic alkylation of a stereoisomeric mixture of 107.
37. Scheme 5.35 Enantioselective decarboxylative allylic alkylation of enediol-derived carbonates 110 and 111. Controlled formation of allylated α-oxy-substituted aldehydes 112 and ketones 114.
38. Scheme 5.36 Rationale for the regiochemical outcome in the decarboxylative allylic alkylation of enediol-derived carbonates 110 and 111.
39. Scheme 5.37 Enantioselective formation of lactams 117 and cyclic imides 119 by decarboxylative allylic alkylation of esters 116 and 118, respectively.
40. Scheme 5.38 Crossover experiment of palladium-catalyzed decarboxylative allylic alkylation reported by Stoltz et al. The authors measured the exact molecular masses by HRMS. The whole numbers are indicated here for reasons of simplification.
41. Scheme 5.39 Opposite topicity in the palladium-catalyzed allylic alkylation of lithium enolate 13b and decarboxylative allylic alkylation of carbonate 103a. The same enantiomer (R)-15 forms with quasienantiomeric ligands (S,S)-14 and (R,R)-69.
42. Scheme 5.40 Inner-sphere mechanism in the decarboxylative allylic alkylation, proposed by Stoltz.
43. Scheme 5.41 Evidence for outer-sphere mechanism in the decarboxylative allylic alkylation, reported by Trost.
44. Scheme 5.42 Visualization of Trost's rationale for the stereochemical outcome in the allylation of an LDA–lithium enolate aggregate (left) and a “naked” enolate (right).
45. Scheme 5.43 Enantioselective palladium-catalyzed decarboxylative allylic alkylation under ring opening of bicyclic racemic ketone 130.
46. Scheme 5.44 Enantioselective formation of butenolides 133 by palladium-catalyzed decarboxylative allylic alkylation of furan-derived enol carbonate 132.
47. Scheme 5.45 Cascade of palladium-catalyzed decarboxylative allylic alkylation and trapping of the palladium enolate, assumed as O-bound tautomer 135, by Michael acceptors.
48. Scheme 5.46 General, simplified catalytic cycle of enolate arylation, mediated by [L_nPd⁰]. The intermediate palladium enolates are assumed to exist as equilibrium of C- and O-bound tautomers 140 and 141, respectively.
49. Scheme 5.47 Enantioselective palladium-catalyzed enolate arylation of racemic aminomethylene ketones 143 mediated by chiral ligands 144.
50. Scheme 5.48 Enantioselective nickel-catalyzed arylation of enolates derived from racemic butyrolactones 147, mediated by (S)-BINAP (23).
51. Scheme 5.49 Palladium- and nickel-catalyzed enantioselective reaction of aryl triflates with enolates derived from racemic ketones 149, catalyzed by palladium or nickel complexes with ligand 150.
52. Scheme 5.50 Enantioselective palladium-catalyzed arylation of enolates derived from racemic oxindoles 152, mediated by the axially chiral and P-stereogenic ligand 153.
53. Scheme 5.51 Enantioselective synthesis of carboxylic esters 156 with a tertiary stereogenic α-carbonyl center by arylation of silyl ketene acetals 155.
54. Scheme 5.52 Enantioselective intramolecular arylation in anilides rac-157 under formation of oxindoles 160.
55. Scheme 5.53 Enantioselective intramolecular enolate arylation of racemic ortho-bromoanilides 161, 163, and 165.
56. Scheme 5.54 Enantioselective intramolecular arylation of aldehydes 167 to 1-formylindanes 168.
57. Scheme 5.55 Enantioselective and diastereoselective aldol addition mediated by the chiral lithium amide 170.
58. Scheme 5.56 Enantioselective enolate formation of tropinone 173 and preparation of β-hydroxy ketone 174 in a diastereoselective aldol addition.
59. Scheme 5.57 Mukaiyama's enantioselective aldol addition of silicon enolates 175a and 178; proposed catalytic cycle.
60. Scheme 5.58 Selection of chiral boron catalysts used for the asymmetric Mukaiyama aldol reaction.
61. Scheme 5.59 Stereoconvergent aldol reaction of silyl enol ethers 186 and 187 mediated by acyloxyborane 182a.
62. Scheme 5.60 Enantioselective aldol addition of silyl ketene O- and S-acetals 191 and 193 mediated by oxazaborolidinone 183. Proposed catalytic cycle.
63. Scheme 5.61 Titanium and zirconium catalysts used for the asymmetric Mukaiyama aldol reaction.
64. Scheme 5.62 Enantioselective Mukaiyama aldol additions mediated by titanium–BINOL complexes 196 according to Mikami and Keck. Proposed Zimmerman–Traxler-type transition state model.
65. Scheme 5.63 Vinylogous aldol addition of silyl dienolate 203a mediated by titanium–BINOL complex; enantioselective synthesis of phorbaside A building block 205.
66. Scheme 5.64 Stereoconvergent aldol addition of silicon enolates mediated by Kobayashi's zirconium complex. Application in the synthesis of khafrefungin building block 210.
67. Scheme 5.65 Carreira's enantioselective aldol reaction of silicon enolates 211 and dienolate 214. Application for the synthesis of macrolactin A building blocks 215 and ent-215.
68. Scheme 5.66 Selection of frequently applied Evans' BOX and PYBOX ligands 216–218.
69. Scheme 5.67 Evans' Mukaiyama aldol and vinylogous aldol reactions mediated by the copper PYBOX catalyst 217; enantioselective synthesis of callipeltoside A building block 225.
70. Scheme 5.68 Proposed catalytic cycle of Evans' enantioselective catalytic aldol addition and model 229 for rationalizing the stereochemical outcome.
71. Scheme 5.69 Stereodivergent Evans' aldol addition mediated by copper complex 216a and tin complex 218. Model 233 for rationalizing the topicity in the copper–BOX-catalyzed aldol reaction.
72. Scheme 5.70 Stereodivergent course in Denmark's aldol addition of silicon enolate 236, mediated by chiral phosphoramides 234a and 234b.
73. Scheme 5.71 Diastereoselective and enantioselective aldol addition of aldehyde-derived trichlorosilyl enolates 241 and 243, mediated by bisphosphoramide 235.
74. Scheme 5.72 Denmark's asymmetric aldol additions of silyl ketene acetals 246 and 248 mediated by silicon tetrachloride and catalyzed by bisphosphoramide 235; proposed catalytic cycle.
75. Scheme 5.73 Application of Denmark's silicon tetrachloride-mediated aldol protocol in a total synthesis of the polyene macrolide RK-379.
76. Scheme 5.74 Diastereoselective and enantioselective Mukaiyama aldol addition catalyzed by doubly lithiated BINOL 262; proposed transition state model 264.
77. Scheme 5.75 Catalytic cycle of the aldol addition of silicon enolates 220 under transmetallation into transition metal enolate 265.
78. Scheme 5.76 Shibasaki–Sodeoka aldol reaction catalyzed by palladium complex 268.
79. Scheme 5.77 Carreira's copper-catalyzed vinylogous aldol addition of silyl dienolate 214; postulated catalytic cycle.
80. Scheme 5.78 Shibasaki's copper-catalyzed aldol addition of silyl ketene acetals to prochiral ketones.
81. Scheme 5.79 Rawal's stereoselective Mukaiyama aldol addition under hydrogen-bonding catalysis.
82. Scheme 5.80 Hayashi's gold-catalyzed direct aldol reaction of isocyano ester 281.
83. Scheme 5.81 Shibasaki's direct aldol reaction mediated by the lanthanum–lithium complex 285; assumed structures of loaded intermediate catalysts 288 and 289.
84. Scheme 5.82 Trost's direct aldol reaction catalyzed by the dizinc complex of ligand 290.
85. Scheme 5.83 Catalytic cycle proposed for the aldol reaction mediated by dizinc complexes of ligand 290.
86. Scheme 5.84 Evans' direct aldol reaction of thiazolidinethione 299, catalyzed by nickel complex 300; proposed catalytic cycle.
87. Scheme 5.85 Nishiama's direct aldol reaction of enones 307, catalyzed by rhodium complex 308; models 310 and 311 for rationalizing the stereochemical outcome.
88. Scheme 5.86 Cozzi's enantioselective Reformatsky reaction, mediated by manganese salen complex 313.
89. Scheme 5.87 Feringa's enantioselective Reformatsky reaction mediated by BINOL-type ligand 315.
90. Scheme 5.88 Enantioselective Reformatsky reaction mediated by amino alcohol 323.
91. Scheme 5.89 Enantioselective difluoro Reformatsky reaction.
92. Scheme 5.90 Kobayashi's Mukaiyama–Mannich reaction of imines 328, mediated by BINOL–zirconium complex 329.
93. Scheme 5.91 Proposed catalytic cycle of Mukaiyama–Mannich reaction mediated by BINOL–zirconium complex 329; stereochemical model 339.
94. Scheme 5.92 Mukaiyama–Mannich reaction of imino esters 340, mediated by copper complex 341; proposed catalytic cycle.
95. Scheme 5.93 Mukaiyama–Mannich reaction of phosphinoyl imines 346 and 350, mediated with copper complexes of ligands 348 and 351, respectively.
96. Scheme 5.94 Mannich and vinylogous Mannich reactions mediated by silver complexes of ligands 354.
97. Scheme 5.95 Mukaiyama–Mannich reaction under proton catalysis of the chiral urea derivative 363.
98. Scheme 5.96 Mukaiyama–Mannich reaction catalyzed by Akiyama's chiral phosphoric acid 367.
99. Scheme 5.97 Sibasaki's Mannich procedure based on zinc complexes of “linked BINOL” 371.
100. Scheme 5.98 Enantioselective and diastereoselective direct Mannich reactions catalyzed by ligands 290.
101. Scheme 5.99 Enantioselective ester enolate–imine condensation mediated by the stoichiometric additive 379.
102. Scheme 5.100 Enantioselective ester enolate–imine condensation mediated by the ligand 383.
103. Scheme 5.101 Cozzi's multicomponent imino Reformatsky reaction.
104. Scheme 5.102 Enantioselective preparation of β-lactams 392 through imino difluoro Reformatsky reaction
105. Scheme 5.103 Evans' Mukaiyama–Michael procedure based on catalyst 216b; proposed catalytic cycle.
106. Scheme 5.104 Correlation of configuration in enolates 401 and 403 with products 402 and 404 in Evans' procedure for conjugate additions.
107. Scheme 5.105 Conjugate addition of silyl enol ethers 405 to crotonylphosphonates 406, mediated by aluminum complex 407.
108. Scheme 5.106 Enantioselective formation of metal enolate 409 in conjugate addition and quenching by protonation. Selection of ligands 410–416 frequently used in enantioselective conjugate addition.
109. Scheme 5.107 Formation of zinc enolate 418 by enantioselective conjugate addition, transmetallation into silicon enolate 419, and oxidation to ketone 420.
110. Scheme 5.108 Simplified tentative catalytic cycle of the copper-catalyzed conjugate addition of dialkylzinc to cyclohexenone.
111. Scheme 5.109 Copper-catalyzed enantioselective conjugate addition of dimethyl zinc and enolate trapping by palladium-catalyzed allylic alkylation to ketone 427. Application to a synthesis of pumiliotoxin C.
112. Scheme 5.110 Copper-catalyzed enantioselective conjugate addition of zinc reagent 429 and aldol addition to cyclopentanone 431. Application to a synthesis of PGE₁ methyl ester.
113. Scheme 5.111 Rhodium-catalyzed enantioselective conjugate addition of phenylboronic acid to cyclohexenone according to Hayashi and Miyaura; proposed catalytic cycles.
114. Scheme 5.112 Rhodium-catalyzed enantioselective conjugate addition and subsequent diastereoselective aldol addition/allylation of boron enolate 438. Model for rationalizing the stereochemical outcome.
115. Scheme 5.113 Rhodium-catalyzed enantioselective conjugate addition and subsequent diastereoselective intramolecular aldol addition to bicyclic ketone 445; transition state model 444.
116. Scheme 5.114 Rhodium-catalyzed enantioselective conjugate addition of vinyl zirconium compounds 446 and subsequent diastereoselective aldol addition.
117. Scheme 5.115 Enantioselective conjugate addition of malonates 448 to cyclopentenone, mediated by Shibasaki's catalyst 449 and subsequent aldol addition. Conversion of adduct 452 into 11-deoxy-PGF_1α.
118. Scheme 5.116 Proposed catalytic cycle of conjugate addition/aldol reaction mediated by the complex 449.
119. Scheme 5.117 Rhodium-catalyzed acrylate reduction followed by an aldol addition.
120. Scheme 5.118 Selected procedures for enantioselective enolate protonation with stoichiometric or overstoichiometric proton sources.
121. Scheme 5.119 Enantioselective enolate with stoichiometric and catalytic amounts of proton source 472. Conversion of thioester 473 into α-damascone. Proposed catalytic cycle.
122. Scheme 5.120 Stoichiometric and catalytic use of imide 476 as a chiral proton source. Proposed catalytic cycle.
123. Scheme 5.121 Enantioselective protonation of silicon enolates 482 and 484 using BINOL monomethyl ether 481 in catalytic amounts; proposed catalytic cycle.
124. Scheme 5.122 Enantioselective protonation of chiral palladium enolates generated by decarboxylation of β-keto esters 487 and 489; simplified proposed catalytic cycle.
125. Scheme 5.123 Mechanism of the enolate oxidation with sulfonyloxaziridines.
126. Scheme 5.124 Selected examples of enantioselective enolate oxidations mediated with chiral sulfonyloxaziridines 501.
127. Scheme 5.125 Conversion of silyl enol ethers 506 and 509 into α-hydroxy ketones 508 and 510, respectively, by Sharpless asymmetric dihydroxylation.
128. Scheme 5.126 Enantioselective oxidation of silicon enolates 512 mediated by salen complex 511b.
129. Scheme 5.127 Ambidoselectivity in the reaction of silicon and tin enolates 514 with nitrosobenzene.
130. Scheme 5.128 Enantioselective silver-catalyzed reaction of tin enolates 518 with nitrosobenzene 515 to α-aminooxy ketones 519 as intermediates for the formation of α-hydroxy ketones.
131. Scheme 5.129 Enantioselective silver-catalyzed reaction of silicon enolates 521 with nitrosobenzene 515 to α-aminooxy ketones 519, mediated by ligand 522. Reagent control in the reaction of enantiomeric silicon enolates 523.
132. Scheme 5.130 Enantioselective copper-catalyzed amination of silicon enolates 526, 529, and 531 with azoimide 527; proposed catalytic cycle.
133. Scheme 5.131 Enantioselective silver-catalyzed enolate amination with azodicarboxylate 535.
134. Scheme 5.132 Regioselective N-attack reaction of tin enolates 537 to nitrosobenzene 515, mediated by BINAP–silver complex 538.
135. Scheme 5.133 Stoichiometric reagents 540 and 541 for enantioselective enolate fluorination.
136. Scheme 5.134 Lectka's enantioselective fluorination of acid chlorides 543 catalyzed by benzoylquinidine 545. “Trifunctional” reaction mechanism.
137. Scheme 5.135 Homocoupling of titanium enolates of oxazolidinone 552, mediated by TADDOL 553.
138. Scheme 5.136 Heterocoupling of octanal with silicon enolates 556, mediated by imidazolidinone 557; model 559 for rationalizing the stereochemical outcome.

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