Activation of carboxyl groups by diphenyl 2-oxo-3-oxazolinylphosphonate. Facile preparation of versatile reagents, 3-acyl-2-oxazolones

Synthetic utility of the 2-oxazolone moiety as an excellent new leaving group is described. Based on such a function of the heterocycles, diphenyl 2-oxo-3-oxazolinylphosphonate [DPPOx] has been newly introduced as a carboxyl-activating reagent which permits a facile direct preparation of 3-acyl-2-oxazolones and amides including peptides from a wide variety of carboxylic acids The 3-acyl-2-oxazolides also serve as versatile reactive agents for highly chemoselective acyl-transfer to the nucleophilic species such as amines, alcohols and thiols, providing convenient and high-yield routes to amides, esters and thiol esters under mild conditions. They are also useful intermediates for ketones and alcohols.