HIGH-TEMPERATURE BROMINATION .8. BROMINATION OF HOMOBENZONORBORNADIENE

The electrophilic addition of bromine to homobenzonorbornadiene (3) at 10 degrees C led in quantitative yield to the formation of di-anti-br omo adduct 4. However, high-temperature bromination of 3 in decalin at 150 degrees C followed by repeated chromatography combined with fract ional crystallization gave us 13 products. Non-rearranged products 5 a nd 6 have been isolated in 34% yield. The formation of allylic bromina ted products 8, 9 and 13 (33%) at high temperature have been discussed in terms of free radical mechanism. 14 and 15 are alcohol compounds w hich arise from hydrolysis of 8, 9, and 13, respectively. All compound s have been characterized properly, especially by 200 MHz H-1 NMR and 50 MHz C-13 NMR and by chemical transformations. Furthermore, it has b een concluded that high temperature bromination of bicyclic systems gi ves more non-rearranged products. Lf the molecule is more strained, th e tendency to rearrange decreases as in the case of benzonorbornadiene . Copyright (C) 1996 Elsevier Science Ltd.