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

The Wittig reaction of ethyl (triphenylphosphoranylidene)acetate ( 2a ) with the carbonyl group of trisubstituted 5(4 H )‐oxazolones 1a – c afforded ethyl 5(4 H )‐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.