α-Pyranones; I. Reaction of 4-ethoxy and 4-chloromethylene-2-phenyl-5(4H)-oxazolone with ethyl 3-oxo-4-(triphenylphosphoranylidene)butyrate: A new synthesis of 2H-pyran-2-one compounds

The reaction of 4-ethoxymethylene-5(4H)-oxazolone (2a) with ethyl 3-oxo-4-(triphenylphosphoranylidene)butyrate (1) affords ethyl 3-benzoylamino-2-oxo-6-triphenylphosphoranylidenemethyl-2H-pyran-5-cah boxylate (3). Starting from the corresponding 4-chloromethylene compound 2b and 1, besides 3, ethyl 3-benzoylamino-6-[2-(4,5-dihydro-5-oxo-2-phenyl-4-oxazolylidene)-1-(tr iphenylphosphoranylidene)ethyl]-2-oxo-2H-pyran-5-carboxylate (5) is formed. The phosphorane 3 is a reactive synthetic intermediate for the preparation of ethyl 6-(1-alkenyl)-3-benzoylamino-2-oxo-2H-pyran-5-carboxylates 7 through reaction with aldehydes.