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 tre ating 2,9-dithia-1-phosphabicyclo[4.3.0]-nona-3,7-dien 1-sulfides with n-Bu3P. The thiaphospholes reacted thermally with norbornadiene, norb ornene or diethyl azodicarboxylate to produce the 1:2 double Diels-Ald er cycloadducts. With a mixture of norbornadiene and methyl acrylate o r acrylonitrile, the crossed double Diels-Alder cycloadducts were obta ined. In the presence of a Lewis acid, the thiaphospholes underwent, a t the initial step, the Diels-Alder reaction with acrylic esters, meth yl vinyl ketone or acrylonitrile, followed in tandem by the Michael ad dition of the 1:1 cycloadducts to another molecule of the reactant.