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-bromo adduct 4. However, high-temperature bromination of 3 in decalin at 150 degrees C followed by repeated chromatography combined with fractional crystallization gave us 13 products. Non-rearranged products 5 and 6 have been isolated in 34% yield. The formation of allylic brominated products 8, 9 and 13 (33%) at high temperature have been discussed in terms of free radical mechanism. 14 and 15 are alcohol compounds which arise from hydrolysis of 8, 9, and 13, respectively. All compounds have been characterized properly, especially by 200 MHz H-1 NMR and 50 MHz C-13 NMR and by chemical transformations. Furthermore, it has been concluded that high temperature bromination of bicyclic systems gives more non-rearranged products. Lf the molecule is more strained, the tendency to rearrange decreases as in the case of benzonorbornadiene. Copyright (C) 1996 Elsevier Science Ltd.