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

Lithium P,P-diphenyl-P-(alkyl)(N-phenyl)phosphazenes act as bidentate reage nts towards electrophilic olefins and acetylenes. The reactions with dimeth yl acetylenedicarboxylate (DMAD) and dimethyl maleate afford cyclopentenone s, while with methyl benzoylpropiolate the products obtained are butenolide s with a quaternary carbon atom in position 5 of the heterocycle. The use o f less activated substrates (methyl phenylpropiolate, methyl cinnamate, and dimethyl oxalate) allowed the isolation of C-acylated aminoylide or phosph azene derivatives. A reaction mechanism is proposed based on a tandem proce ss involving the regioselective C-acylation of the carbon alpha to the phos phorus, followed by a cyclisation process promoted by the intramolecular Mi chael addition of the nitrogen of the PN linkage to an electrophilic double or triple carbon-carbon bond.