REACTIONS AND REACTIVITY OF ACYLOXYCARBENES

Phenylacetoxycarbene, phenyl(pivaloyloxy)carbene, and phenyl(benzoylox y)carbene, photolytically generated from diazirine precursors in penta ne at 25 degrees C, efficiently rearranged by 1,2-acyl migrations to g ive high yields of the appropriate 1,2-diketones. The kinetics of thes e rearrangements were determined by laser flash photolysis. Substituen t effects on the acyl migrations and ab initio electronic structure ca lculations on ground state carbenes and transition states were employe d to analyze the rearrangement mechanism. Additions of phenylacetoxyca rbene to alkenes proceeded in good yields, in lieu of the 1,2-acyl shi ft; absolute rate constants were obtained for these reactions of the a mbiphilic carbene. (Phenoxymethyl)acetoxycarbene gave only a 1,2-H shi ft; the potentially competitive 1,2-acetyl migration was suppressed.