Photocyclization Reactions. Part 3 [1]. Synthesis of Naphtho[1,8-bc]-furans and Cyclohepta[cd]benzofurans Using Photocyclization of 8-Alkoxy-1,2,3,4-tetrahydro-1-naphthalenones and 4-Alkoxy-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ones

Article abstract of DOI:10.1002/jhet.5570330104

Photocyclization reactions were carried out on 8-alkoxy-1,2,3,4-tetrahydro-1-naphthalenones (six-membered ring ketones) 4a-g and 4-alkoxy-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ones (seven-membered ring ketones) 5a-e in acetonitrile. Irradiation of 4a-f gave rearranged naphthyl alcohols 8a-f as major products. In the case of 4g, 2a,3,4,5-tetrahydronaphtho[1,8-bc]furan-2a-ol 6g was obtained. In contrast, irradiation of 5a-e afforded 2,2a,3,4,5,6-hexahydrocyclohepta[cd]benzofuran-2a-ols 9a-e in good yields. The difference in reactivities between 4a-g and 5a-e is attributed to the conformation of six- and seven-membered rings. Conformational and substituent effects in cyclization step of 1,5-biradicals are discussed along with reaction pathways.