High-Temperature Bromination .6. Bromination of Benzobarrelene

Abstract

The electrophilic addition of bromine to benzobarrelene in chloroform at 10 degrees C followed by repeated chromatography combined with fractional crystallization allowed us to isolate ten products 12-21 Structural determination of these compounds revealed that the barrelene skeleton was rearranged completely. 18-21 are alcohol compounds which arise from hydrolysis of 12, 13, 14, and 15 respectively. High temperature bromination of benzobarrelene in decalin at 150 degrees C followed by repeated chromatography combined with fractional crystallization gave us 18 products. Nonrearranged products 24, 25, and 26 have been isolated in 50% yield. All compounds have been characterized properly, especially by 200 MHz H-1 NMR and 50 MHz C-13 NMR spectra. Furthermore, it has been concluded that high temperature bromination of bicyclic systems gives more non-rearranged products if the molecule is more strained, the tendency to rearrange decreases as in the case of benzonorbornadiene.