Ketene. Part 25. Mechanistic studies of the reaction of nitrile oxides with ketenes

Abstract

The reaction of ¹⁷O-labelled 2,4,6-trimethylbenzonitrile N-oxide (4) with dimethylketene gives the dihydro-oxazolone adduct (5b), with isotopic labelling predominantly, but not exclusively, in the carbonyl group. Thermal scrambling of the label is observed, presumably via the zwitterion (6). The dioxazole (8) is proposed as an intermediate in the conversion of (4) into (5b). Alkaline hydrolysis of (5b) gives (10b) by predominant hydroxide attack on the carbonyl group. Attempts to generate the α-lactone (11)(by thermal decomposition of alkali α-halogenoisobutyrates) and add it to benzonitrile and fluorenone anil were unsuccessful. No traces of compounds (5; Ar = Ph, R = Me) or (2; R¹= Ph, R = Me) could be detected, suggesting that α-lactones are not intermediates in the formation of adducts of dimethylketene with nitrile oxides and nitrones.