Ketene. Part 23. Conformational control of the addition reactions of ketenes with N-phenylnitrones

Abstract

X-Ray analysis shows that the nitrone group in (5a) is not distorted, disproving a previous explanation for the formation of oxazolidinones rather than indolones in the reactions with ketenes. Nitrone (5c) reacts with dimethylketene and diphenylketene to form oxazolidinones (6c,d) whereas nitrones (5d) and (5e) under similar conditions form indolone derivatives (9). Oxazolidinone formation by the reaction of ketenes with nitrones (5a–c) results from restricted rotation about the N-phenyl bond preventing the [3,3]-migration (3)→(4), which precedes indolone formation.