5‐Oxazolones, IV. Reactions of 5(4H)‐oxazolones with triphenylphosphonium methylides

The Wittig reaction of ethyl (triphenylphosphoranylidene)acetate (2a) with the carbonyl group of trisubstituted 5(4H)-oxazolones 1a–c afforded ethyl 5(4H)-oxazolylideneacetates 3a–c and triphenylphosphane oxide. Starting from oxazolones 1d–i and ylide 2a, methyleneoxazoles 3d, e and ethyl 5-oxazoleacetates 4a–f were obtained besides ylides 5a–e deriving from the nucleophilic attack of the ylide at 1 and subsequent opening of the oxazole ring. Oxazolones 1a–c reacted also with triphenylphosphonium phenylmethylide (2b) to yield methyleneoxazoles 3f,g and ylides 5f–h. By treating triphenylphosphonium methylide (2c) and -methoxymethylide (2d) with 1a–c only open-chain compounds 5i–k and 5l–n, respectively, were obtained.