Synthesis of Alkyl 6-(2-Alkoxy-2-oxoethyl)dibenzo[d,f][1,3]dioxepine-6-carboxylates from Stabilized Phosphorus Ylides

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by biphenyl-2,2′ -diol leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce the corresponding stabilized phosphorus ylides. Magnesium oxide powder was found to catalyze the conversion of the stabilized phosphorus ylides to alkyl 6-(2-alkoxy-2-oxoethyl)dibenzod,f]1,3]dioxepine-6-carboxylates in solvent-free conditions under microwave (0.5 KW, 3 min) and thermal (90 °C, 60 min) conditions.