New, Simple and Versatile Synthesis of Protected (alpha)-Alkylidene-(beta)-amino Acids from Activated Vinylphosphonates

A two-step route to Boc-protected (alpha)-alkylidene-(beta)-amino esters was developed by addition of sodium tert-butylcarbamate to ethyl 2-diethoxyphosphoryl-2-alkenoates followed by the Horner-Wadsworth-Emmons olefination of aldehydes using intermediate 2-diethoxyphosphoryl-3-tert-butoxycarbonylaminoalkanoates.