PALLADIUM-CATALYZED TRANSPROTECTION OF ALLYLOXYCARBONYL-PROTECTED AMINES - EFFICIENT ONE-POT FORMATION OF AMIDES AND DIPEPTIDES

The synthetic utility of the N-(allyloxycarbonyl) (Alloc) substituent in alpha-amino acid derivatives is substantially extended beyond its w ell-known function as an amine protecting group. When the palladium-ca talyzed deprotection is carried out by using tributyltin hydride as nu cleophile (the Guibe method) in the presence of an active acylating ag ent a new acyl group is introduced on nitrogen. Successful acylating a gents include carboxylic acid anhydrides, acid chlorides, and activate d esters. A useful example of this methodology is the removal of the A lloc group in the presence of tert-butyl dicarbonate, which in essence amounts to a ''transprotection'' to a Boc-protected alpha-amino acid derivative. More importantly, the use of activated N-protected alpha-a mino ester derivatives (e.g., pentafluorophenyl esters) leads to dipep tides. This new method for peptide coupling proceeds very fast under m ild conditions, in good to excellent yields, and without noticeable ra cemization.