Use of arene 1,3-substituents to control cyclopropane ring formation during meta photocycloaddition of ethenes to the benzene ring

Abstract

The 3-trifluoromethyl derivatives of benzyl alcohol, benzyltrimethylsilane and phenoxytrimethylsilane undergo 2,6-photocycloaddition to cyclopentene to give the 1,11-disubstituted-tetracyclo[6.3.0.0^2,11.0^3,7]undec-9-enes 7, 10, 11 and 12. This specificity in isomer formation is considered to originate from an intramolecular attractive interaction between the 1,3-substituents on the arenes during the addition of the ethene and this causes an asymmetric distortion of the C₆ ring which then controls the cyclopropane ring formation in the adduct. Similar reaction of 3-trifluoromethyl-phenol, -benzyl alcohol and -benzyltrimethylsilane, with vinyl acetate yields the 2-trifluoromethyl-endo-6-acetoxytricyclo[3.3.0.0^2,8]oct-3-enes 16, 17 and 18 respectively, showing that the directing influence of substituents on the arene dominates any effect of the acetoxy group on the photocycloaddition process. The control by Si· · ·F interaction is not, however, significant during the intramolecular photocycloaddition of the bichromophores 19 and 20 and only the 1,6-bridged dihydrosemibullvalene 24 and products derived from ortho cycloaddition are respectively formed.