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Abstract
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Reaction of triphenylphosphine with dialkyl acetylenedicarboxylates in the presence of strong CH-acids such as acetylacetone, methyl acetoacetate, cyclopentane-1,3-dione, or 5,5-dimethylcyclohexane-1,3-dione (dimedone) have been studied. In some cases, stable phosphorus ylides are obtained in excellent yields. The ylide moiety of these compounds is strongly conjugated with the adjacent carbonyl group and rotation about the partial double bond in (E) and (Z) geometrical isomers is slow on the NMR time scale at ambient temperature. Thus, these ylides exist as a mixture of geometrical isomers. From the reaction of dimedone with dimethyl acetylenedicarboxylate (DMAD) in the presence of triphenylphosphine, a chromene derivative is obtained. A Michael addition product was obtained from the reaction of cyclopentane-1,3-dione and DMAD
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