FORMATION OF SELENOCARBONYL COMPOUNDS BY THE USE OF PHOSPHORUS YLIDES - SYNTHESIS AND REACTIONS OF SELENOBEUZOPHENONES

This paper describes the reaction of phosphorus ylides with chalcogen compounds. Thioaldehydes were formed by the reaction of phosphorus ylides with thiirane or elemental sulfur, which further reacted with dienes to afford the corresponding cycloadducts. Thioaldehydes were also found to react with secondary amines to give the corresponding thioamides. 4,4'-Dimethoxy- and 4,4'-dimethylselenobenzophenone could be isolated in moderate yields by the reaction of diarylmethylenetriphenylphosphoranes with elemental selenium in toluene at 90 degrees C. Attempted isolation of unsubstituted selenobenzophenone afforded only its dimer. The oxidation and thiation of 4,4'-dimethoxyselenobenzophenone afforded the corresponding benzophenone and thiobenzophenone in good yields. The reaction of selenobenzophenone with cyclopentadiene afforded the corresponding cycload ducts (3,3-diaryl-2-selenabicyclo[2.2.1]hept-5-ene) whereas bicyclic diselenides(4,4-diaryl-2,3-diselenabicyclo[3.3.0]oct-7-ene) were obtained by using excess selenium and higher temperature. The reaction of 4,4'dimethoxyselenobenzophenone with benzenediazonium carboxylate afforded 2,2-di(4-methoxyphenyl) benzo-1,3-oxaselenane. Other reactions were also described.