Application of the addition of triorganozincates to N-(tert-butanesulfinyl)imines to the enantioselective synthesis of α-amino acids

Highly enantiomerically enriched N-protected alpha-amino acids can be easily prepared from optically pure N-(tert-butanesulfinyl)imines by a four-step sequence involving: diastereoselective addition of a triorganozincate to the imine, removal of the sulfinyl group, benzoylation of the nitrogen atom of the obtained primary amine and oxidation of one of the substituents on the carbon atom alpha to the nitrogen. Using the same configuration in the sulfinyl chiral auxiliary, amino acids with the (R) or the (S) configuration can be prepared by choosing the proper combination of imine and organozincate. alpha,alpha-Disubstituted alpha-amino esters with high optical purity can also be prepared by the diastereoselective addition of trialkylzincates to alpha-imino esters. (C) 2009 Elsevier Ltd. All rights reserved.