Exceptionally simple homologation of protected α- to β-amino acids in the presence of silica gel

The Wolff rearrangement of alpha-amino acid-derived diazoketones is simply achieved by gentle warming in a ethyl acetate/silica gel slurry containing catalytic amounts of silver trifluoroacetate. Without workup (not counting filtration and evaporation) the protected beta-amino acids are obtained in high yields (92-97%) without significant impurities. This variation avoids the laborious workup after a conventional silver-catalyzed Wolff rearrangement. This method can be similarly applied to the synthesis of beta-amino acid methyl esters when methanol is used as solvent. No reaction occurs without silica gel.