SYNTHESES OF 1,2-THIAPHOSPHOLES AND THEIR THERMAL AND LEWIS ACID-PROMOTED ADDITION-REACTIONS

3,5-Di-substituted 1,2-thiaphospholes were efficiently prepared by treating 2,9-dithia-1-phosphabicyclo[4.3.0]-nona-3,7-dien 1-sulfides with n-Bu3P. The thiaphospholes reacted thermally with norbornadiene, norbornene or diethyl azodicarboxylate to produce the 1:2 double Diels-Alder cycloadducts. With a mixture of norbornadiene and methyl acrylate or acrylonitrile, the crossed double Diels-Alder cycloadducts were obtained. In the presence of a Lewis acid, the thiaphospholes underwent, at the initial step, the Diels-Alder reaction with acrylic esters, methyl vinyl ketone or acrylonitrile, followed in tandem by the Michael addition of the 1:1 cycloadducts to another molecule of the reactant.