No 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 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.

The formation of isomers from the inter-and intra-molecular meta photocycloaddition of ethenes to the benzene ring has been specifically directed using the addend substituents in order to cause an asymmetric distortion of the C6 ring during the reaction, and to induce non-synchroneity into the addition process. The latter influence in the intramolecular reaction is achieved by the prese~ace of a heteroatom in the linking tether which also provides a convenient access to linear and angular heterotriquinanes. The meta photoaddition can be induced by sunlight exposure of appropriately substituted arene-ethene bichromophores.

Use of Arene 1,3-Substituents to Control Cyclopropane Ring Formation During meta Photocycloaddition of Ethenes to the Benzene Ring -[e.g. intermolecular meta photocycloaddition of arenes (I) with ethene derivatives (II) and (IV)]. -(AMEY, D. M.; GILBERT, A.; JONES, D. T.; J. Chem. Soc., Perkin Trans. 2 [old] (1998) 2, 213-218; Dep. Chem., Univ. Reading, Whiteknights, Reading, Berkshire RG6 2AD, UK; EN)