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 C 6 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.

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Abstract. The photoreactions of the methylbenzonitriles; 2,3-, 2,4-, 2,6-, 3,4-, and 3 3 -benzonitriles; and 2'-and 4'-methoxyacetophenones with cyclopentene and ethyl vinyl ether have been investigated. Meta photocycloaddition is the major process for the benzonitriles with cyclopentene, and regiochemical features reflect the influence of polar factors along the reaction pathway. The enol ether yields ortho cycloadducts exclusively from all the benzenoid derivatives. The thermal ring opening of the primary photoadduct and the photolability of the cycloocta-1,3,5-triene isomer depend markedly on the position of the substituents.

1996bridged compounds bridged compounds Q 0060 -083Formation of Bicyclo(3.2.1)oct-2-en-8-ones and 1-Hydroxydihydrosemibullvalenes from the meta-Photocycloaddition of Cyclopentene to Phenols.

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