Synthesis of cyclopentenones and butenolides by reaction of the lithium salt of P,P-diphenyl-P-(alkyl)(N-phenyl)phosphazenes with electrophilic double and triple bonds

Abstract

Lithium P,P-diphenyl-P-(alkyl)(N-phenyl)phosphazenes act as bidentate reagents towards electrophilic olefins and acetylenes. The reactions with dimethyl acetylenedicarboxylate (DMAD) and dimethyl maleate afford cyclopentenones, while with methyl benzoylpropiolate the products obtained are butenolides with a quaternary carbon atom in position 5 of the heterocycle. The use of less activated substrates (methyl phenylpropiolate, methyl cinnamate, and dimethyl oxalate) allowed the isolation of C-acylated aminoylide or phosphazene derivatives. A reaction mechanism is proposed based on a tandem process involving the regioselective C-acylation of the carbon α to the phosphorus, followed by a cyclisation process promoted by the intramolecular Michael addition of the nitrogen of the PN linkage to an electrophilic double or triple carbon–carbon bond.