Photo-induced molecular transformations. Part 87. Ring expansion through [2 + 2] photocycloaddition-β-scission sequences; synthesis of benzohomotropones from 1- and 2-naphthols and methyl acrylate

Abstract

Photolysis of 4-substituted tricyclo[6.4.0.0^2,5]dodeca-1(12),6,8,10-tetraen-5-ols (9), (10), and (12), derived in three-steps from the regioselective photocycloadducts formed from 2-naphthyl trimethylsilyl ether and methyl acrylate, in the presence of HgO–I₂ in benzene, to give the benzocyclo-octenone derivatives (11), (13), and (14) which arise from β-scission of their fused bond. The benzocyclo-octenones cyclized with base in DMF to give benzohomotropones, 4-substituted tricyclo[6.4.0.0^2,4]dodeca-1(12),6,8,10-tetraen-2-ones (15) and (16). Similar photolyses of 3-substituted tricyclo[6.4.0.0^2,5]dodeca-1(12),6,8,10-tetraen-2-ols (24) and (25), prepared in three steps from the regioselective [2 + 2] photocycloadduct (19) formed from 1-naphthyl trimethylsilyl ether with methyl acrylate, in the presence of HgO–I₂ in benzene, gives the benzocyclo-octenone (26) in rather low yield. Treatment of the latter with a base in DMF gave a benzohomotropone, 3-substituted tricyclo[6.4.0.0^3,5]dodeca-1(12),6,8,10-tetraen-2-one (27).