Photocycloaddition Reactions of Alkyl and Aryl 2-Thioxo-3H-benzoxazole- 3-carboxylates to Alkenes
作者:Takehiko Nishio、Kiyoko Shiwa、Masami Sakamoto
DOI:10.1002/1522-2675(200208)85:8<2383::aid-hlca2383>3.0.co;2-e
日期:2002.8
The photochemical reactions of alkyl and aryl 2-thioxo-3H-benzoxazole-3-carboxylates 1 have been examined. Irradiation of 1 in the presence of tetra- and trisubstituted alkenes 2a and 2b, 2-methylprop-2-ene nitrile 2e, and dienes 2f and 2g gave [2+2] cycloadducts of the C=S bond of 2-thioxobenzoxazoles and the C=C bond of alkenes, spiro[benzoxazole-thietanes] 3, 4, 8-13, 15, 18, 20, 23-26 in moderate-to-good yields. The photoaddition reactions proceed in a regiospecific manner. The spirocyclic compounds obtained are indefinitely stable at room temperature. Irradiation of la in the presence of 1,1- and 1,2-disubstituted alkenes 2c and 2d yielded the products 5-7 of oxazole-ring cleavage. Compound 1d also underwent photoaddition with alkenes to yield spiro[benzoxazole-thietanes] and/or 2-substituted benzoxazoles and/or iminothietanes, depending on the nature of the substituents present in the alkenes. On intramolecular [2 + 2] photoadduct, tetracyclic 27, was obtained, when ethenyl 2-thioxobenzoxazole-3-carboxylate 1e was irradiated.