Regioselective synthesis of 4- and 5-oxazole-phosphine oxides and -phosphonates from 2H-azirines and acyl chlorides

A simple and efficient regioselective synthesis of 4-oxazole-phosphine oxides and -phosphonates from 2H-azirine-phosphine oxides and -phosphonates is described. The key step for the synthesis of oxazoles is a base-mediated ring closure of vinylogous α-aminophosphorus compounds derived from phosphine oxides and from phosphonates . These derivatives and are obtained by reaction of functionalized azirines and with acyl chlorides and subsequent acid-catalyzed ring opening of N-acylaziridine-phosphine oxides and -phosphonates . Regioselective thermal ring cleavage of N-acylaziridine-phosphine oxides leads α-chloro-β-(N-acylamido)-phosphine oxides and their treatment with bases gives 5-oxazole-phosphine oxides .