Asymmetric syntheses. Part 10. The synthesis and reduction of N-phenylazomethines with a lithium aluminium hydride–3-O-benzyl-1,2-O-cyclohexylidene-α-D-glucofuranose complex to give optically active secondary amines

Abstract

A series of N-phenylcyanoamines and N-phenylazomethines have been synthesised. The n.m.r. spectra show mesomeric shielding of the Me protons in azomethines by para-halogen substituents in the order Br > Cl > F H, but protonated azomethines show shielding Br > Cl > F = H. The asymmetric reduction of four of these azo-methines with a lithium aluminium hydride–3-O-benzyl-1,2-O-cyclohexylidene-α-D-glucofuranose complex gives optically active secondary amines. The absolute configuration of N-(α-phenylethyl)aniline was assigned as S by N-phenylation of S-(–)-α-phenylethylamine and hence all these laevorotatory secondary amines obtained by this asymmetric reduction are assigned the S-configuration.