13-Substituted naphthene(K 1)xanthene(or thioxanthene)-1,4-dione (4a, b) have been obtained by thermal cycloaddition of p-benzoquinone (2) to 9-vinylidenexanthene(or thioxanthene) derivatives (1 a, b). Reductive acetylation of 4 gives the diacetoxy derivatives. Compound 4 acting as dienophile, react with 1 or with 1,1-di(p-methoxyphenyl) ethylene (6) to give diadducts. 1,4-Naphthoquinone (10) reacts similarly with 1 to give 14-substituted anthracene(K 1)xanthene(or thioxanthene) 5,15-diones (11a, b). Compounds 1 a, b also react with N-phenylmaleimide (12) to give the diadducts (3a, 3b, 4, 6a, 12, 12a) hexahydro-12-phenyl-N-phenylphthalimido(K 1)xanthene (or thioxanthene) 4-6a-N-phenylpyrrolidine-r,3'-diones (13) or aromatized monoadducts 12-substituted-N- phenylphthalimide (K1) -xanthene (15 a, b).
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