The influence of catalysts on the rearrangement of acyldiazoethanes

Abstract

Contrary to previous findings, decomposition of α-diazo-p-nitropropiophenone by silver oxide is slow at room temperature, and, rather than providing p-nitrophenyl vinyl ketone, yields 3-methyl-3,5-bis-p-nitrobenzoyl-Δ²-pyrazoline (VI). At higher temperatures, silver oxide-assisted Wolff rearrangement sets in. In contrast, decomposition by silver nitrate is much more rapid and leads to p-nitrophenyl vinyl ketone together with smaller amounts of the pyrazoline (VI) and 1-methyl-1,2-bis-p-nitrobenzoylcyclopropane (VII). When molar rather than catalytic quantities of silver nitrate are used, decomposition is virtually instantaneous and the unsaturated ketone is obtained in high yield. Other α-diazopropiophenones behave similarly. The fact that similar decompositions may be effected with silver trifluoroacetate, many metallic nitrates, and aniline hydrochloride, but not by silver benzoate or trimethylamine hydrochloride, suggests that the reaction is one of acid catalysis rather than specific silver catalysis. The results obtained by decompositions effected by nitric, perchloric, and formic acids support this view.