Enantioselective Synthesis of Quaternary l-Valine Derivatives

Significance

The authors present an enantioselective synthesis of l-valine derivatives using the memory of chirality from tertiary aromatic amides incorporated onto l-valine. Alkylation of these derivatives is performed by using a strong base (KHMDS) and reactive electrophiles (such as triflates), though less reactive electrophiles can be used with DMPU as an additive. Reaction times are short to decrease racemization of the enolate and increase ee values. The ee values can be improved by recrystallization for all compounds.