Acyl iodides and bromides give in reaction with ylides 1 the expected 4-C- or O-acylation products 2 or 3. In contrast to acyl ioides and bromides, acyl chlorides give in reaction with the ylides 1 Witting-like reaction products 4(4-(1-chloroalkylidene)-5(4H)-oxazolones), whereas benzoyl fluoride gives 4-(1-benzoyloxybenzylidene)-5(4H)-oxazolones. Some evidence points to a mechanism of the formation of Witting-like reaction products involving O-acylated ylides as intermediates.
