The effect of onium salt additives on the Diels-Alder reactions of a 1-phenyl-1,2-dihydrophosphinine oxide under microwave conditions

The microwave absorbing ability of toluene is increased in the presence of a slight amount (2-4 mg/3 mL) of quaternary ammonium or phosphonium salts. These additives somewhat accelerated the Diels-Alder reaction of 1-phenyl-1,2dihydrophosphinine oxide 1 with N-phenylmaleimide and maleic acid anhydride to afford phosphabicyclo[2.2.2] octene derivatives.