Convenient and simple homologation of N-alpha-urethane protected alpha-amino acids to their beta-homologues with concomitant o-nitrophenylesters formation

The Wolff rearrangement of alpha -aminodiazoketones derived from N-alpha-ur ethane protected alpha -amino acids in presence of o-nitrophenol catalyzed by silver acetate at low temperature is described. The potential utility of the well-known ketene intermediate is exploited for the synthesis of cryst alline, optically pure beta -amino acid active esters. Thus the homologatio n of Boc-/Z-/Fmoc-alpha -amino acids to beta -amino acids with concomitant formation of the corresponding o-nitrophenyl esters has been achieved by th is method. All the beta -amino acid active esters have been obtained in goo d yield and purity and fully characterized by IR and NMR spectra.