Use of arene 1,3-substituents to control cyclopropane ring formation during meta photocycloaddition of ethenes to the benzene ring
作者:David M. Amey、Andrew Gilbert、Damian T. Jones
DOI:10.1039/a707812i
日期:——
The 3-trifluoromethyl derivatives of benzyl alcohol, benzyltrimethylsilane and phenoxytrimethylsilane undergo 2,6-photocycloaddition to cyclopentene to give the 1,11-disubstituted-tetracyclo[6.3.0.02,11.03,7]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[3.3.0.02,8]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.
苄醇、苄基三甲基硅烷和苯氧基三甲基硅烷的 3-三氟甲基衍生物与环戊烯发生 2,6- 光环加成反应,生成 1,11-二取代-四环[6.3.0.02,11.03,7]十一-九-烯 7、10、11 和 12。异构体形成的这种特异性被认为是由于在乙烯的加成过程中,炔烃上的 1,3 取代基之间产生了分子内吸引力相互作用,从而导致 C6 环发生不对称变形,进而控制了加合物中环丙烷环的形成。3-三氟甲基苯酚、-苄基醇和-苄基三甲基硅烷与乙酸乙烯酯发生类似反应,分别生成 2-三氟甲基-内-6-乙酰氧基三环[3.3.0.02,8]辛-3-烯 16、17 和 18,这表明取代基对炔烃的定向影响主导了乙酰氧基对光环化过程的影响。不过,在双溴烯 19 和 20 的分子内光环加成过程中,Si - -F 相互作用的控制作用并不明显,只分别形成了 1,6 桥接的二氢塞布戊烯 24 和正交环加成生成的产物。