Chemoselectivity in reactions of an α-diazo-β-diketone with some conjugative double-bond systems

Abstract

Reactions of 2-diazo-1,3-diphenylpropane-1,3-dione with α,β-unsaturated aldehydes and ketones, and keto-imines, in refluxing anhydrous toluene indicate that benzoyl(phenyl)ketene, which is generated by the thermal Wolff rearrangement of 2-diazo-1,3-diphenylpropane-1,3-dione, shows a pronounced tendency to form chemospecific [2 + 4] Diels–Alder adducts with the carbonyl group in α,β-unsaturated aldehydes and ketones, and the imine group in keto-imines. The reactivity in reactions of the α-diazo-β-diketone with these conjugative double-bond systems is CN > CO > CC. However, benzoyl(phenyl)ketene reacts with α,β-unsaturated imines to produce chemospecific [2 + 2] cycloadducts: β-lactams.