DIELS-ALDER REACTIONS OF DIARYL THIOKETONES WITH DIENOPHILES

Thiobenzophenone and its 4,4'-dichloro derivative combine as dienes (C =S + aromatic CC bond) with dimethyl acetylenedicarboxylate, methyl pr opiolate, dicyanoacetylene, and cyclo-octyne furnishing 1H-2-benzothio pyrans 10, 11, 13, 14; the primary [4+2] cycloaddition is followed by 1,3 prototropy. In the case of the strained (E)-cyclooctene as a dieno phile, the initial nonaromatic cycloadducts 19 were isolated and rearo matized by base catalysis. - In the MS of the 1H-2-benzothiopyrans, M( +) and [M(+) - Ar] are preeminent, both as results of benzylic cleavag e. Copyright (C) 1996 Elsevier Science Ltd