A PEPTIDE ALUMINUM COMPLEX AS A NOVEL CHIRAL LEWIS ACID - ASYMMETRIC ADDITION OF CYANOTRIMETHYLSILANE TO ALDEHYDES

The enantioselective addition of cyanotrimethylsilane (TMSCN) to aldehydes promoted by the addition of a stoichiometric or catalytic amount of organoaluminum complexes of dipeptide esters or alpha-amino acid amides whose amino terminals are modified by a variety of protective groups is described. The reaction of benzaldehyde with TMSCN in the presence of a stoichiometric or catalytic amount of the complex prepared from N-[2-hydroxy-1-naphthyl)methylene]-(S)-valyl-(S)-phenylalanine methyl ester (1a) or N-1(2-hydroxy-1-naphthyl)-methylene]-(S)-valine cyclohexylamide (2a) and trimethylaluminum gives (R)-mandelonitrile in good yield with enantioselectivity as high as 71%. The reaction of cyclohexanecarbaldehyde in the presence of the aluminum complex of N-(1-methyl-2-acetyl-vinyl)-(S)-valine cyclohexylamide (3b) furnishes the corresponding (R)-cyanohydrin in 38% ee, and the reaction of 2,2-dimethylpropionaldehyde with the aluminum complex of N-(4-toluene-sulfonyl)-(S)-valyl-(S)-phenylalanine methyl ester (4a) gives the corresponding (S)-cyanohydrin in 67% ee.