5-Oxazolones. Part V. Reaction of 4-alkylidene-5(4h)-oxazolones with ethyl 3-oxo-4-triphenylphosphoranylidene-butyrate

One-Pot Cyclizations of (2,4-Dioxobutylidene)phosphoranes and (2-Alkoxy-4-oxobut-2-enylidene)phosphoranes

“…The reaction of phosphorane 3a with oxazolones 61 afforded a mixture of dihydrobenzoxazoles 62 and of diastereomeric cyclohexane-1,3-dione ylides 63 and 64 (Table 9). 57 The formation of the resonance-stabilized ylides 63 and 64 is a result of a ring transformation. Instead of the elimination of triphenylphosphine oxide, cleavage of the oxazolone ring of intermediate A took place.…”