Furan-2(3H)- and -2(5H)-ones. Part 7.1 Photochemical behaviour of tetrahydro- and hexahydro-isobenzofuran-1-one systems: a mechanistic and exploratory study

Abstract

The photoreactivity of two variations of the di-π-methane system involving the tetrahydro- and hexahydro-isobenzofuran structures 10 and 11 have been examined and compared with those of β-apolignans 1. The former, 9-phenyl-1,3,4,5,6,7,8,9-octahydronaphtho[2,3-c]furan-1-one 10a and 7-phenyl-1,3,4,7-tetrahydroisobenzofuran-1-one 10b, gave primarily the di-π-methane rearrangement products 18a and 18b, respectively, while the hexahydro substrate, 7-phenyl-1,3,4,5,6,7-hexahydroisobenzofuran-1-one 11, afforded mainly the photoreduced products 21–24. This difference in chemoselectivity is explained in terms of the variant configuration of the phenyl group, an axially orientated one migrating most effectively. A new pathway for the reaction leading to the cyclopropano product 18a or 18b, by way of another cyclopropano derivative 19a or 19b, respectively, is described.