Preparation of 4-[Bis(tert-butoxy)phosphorylmethyl]-N-(fluoren-9-ylmethoxycarbonyl)-DL-phenylalanine. A Hydrolytically Stable Analogue of O-Phosphotyrosine Potentially Suitable for Peptide Synthesis

Sodium methoxide catalyzed aldol condensation of ethyl α-azidoacetate with 4-[bis-(tert-butoxy)phosphorylmethyl]benzaldehyde (4) provides methyl α-azido-4-[bis(tert-butoxy)phosphorymethyl]cinnamate (5), which undergoes facile hydrogenation in the presence of 10 % palladium on carbon to yield methyl 4-[bis(tert-butoxy)phosphorylmethyl]-DL-phenylalaninate (6)