Synthesis of .alpha.-substituted .alpha.-amino acids via cationic intermediates

Abstract

A novel synthetic approach to racemic α-substituted α-amino acids is described. The key intermediates of this methodology are highly electrophilic iminium ions, bearing carbonyl substituents at both the iminium carbon and nitrogen atom. The preparation of precursors 8, 10a-c, and 12 includes electrochemical oxidation techniques according to literature pressures. When an α-methyl precursor (8 or 10a) was used, reactions with sylsilanes and silyl enol ethers led to the desired products, but elimination to dehydroalanine derivatives appeared to be an important side reaction. A major improvement in the yields of the desired products could be effected by using longer reaction times