Asymmetric Catalysis of Carbon-Carbon Bond-Forming Reactions Using Metal(salen) Complexes

Abstract The use of metal(salen) complexes in the asymmetric syntheses of cyanohydrins and amino acids have been developed as important and reliable methods of obtaining these highly versatile chiral intermediates. Thus, we have developed a number of titanium and vanadium(salen) complexes, with ligands derived from (R,R)-cyclohexane-1,2-diamine, which catalyze the synthesis of enantiomerically enriched O-protected cyanohydrins from various carbonyl compounds and cyanide sources. Nickel, copper and cobalt(salen) complexes have also been developed, as catalysts for the preparation of non-racemic amino acids under phase-transfer conditions. 1 Introduction 2 Ti(IV)(salen) Complex-Catalyzed Asymmetric Cyano­hydrin Synthesis 2.1 Synthesis of O-Trimethylsilyl Cyanohydrin Ethers Using Ti(IV) Schiff Base Complexes 2.2 Synthesis of O-Acetyl Cyanohydrins Using Bimetallic Ti(IV)(salen) Complex 15 2.3 Synthesis of Cyanohydrin Ethyl Carbonates Using ­Bimetallic Ti(IV)(salen) Complex 15 2.4 Mechanistic and Kinetic Studies on Bimetallic Ti(IV) ­Complex 15 3 V(V)(salen) Complex-Catalyzed Asymmetric Cyanohydrin Synthesis 4 Synthesis of O-Trimethylsilyl Cyanohydrins Using a ­Heterobimetallic Ti(IV)-V(V)(salen) Complex 5 Formation of α,α-Disubstituted Amino Acids Catalyzed by Nickel(salen) Complexes 6 Formation of Amino Acids Catalyzed by Copper(salen) Complexes 6.1 Influence of the Base on the Enantioselectivity of the ­Alkylation Reaction 6.2 Influence of the Alkylating Agent on the Enantioselectivity of the Alkylation Reaction 6.3 Influence of the Substrate on the Enantioselectivity of the Alkylation Reaction 6.3.1 Influence of the Amino Acid within the Substrate 6.3.2 Influence of the Aryl Group in the Imine Substrate 6.4 Influence of the Catalyst Structure on the Enantioselectivity of the Alkylation Reaction 6.4.1 Influence of the Diamine Structure on the Enantio­selectivity of the Alkylation Reaction 6.4.2 Influence of Aryl Substituents on the Enantioselectivity of the Alkylation Reaction 6.5 Influence of the Mode of Preparation of Complex 38 on the Enantioselectivity of the Alkylation Reaction 7 Formation of α,α-Disubstituted Amino Acids Catalyzed by Cobalt(salen) Complexes 8 Conclusions