High temperature bromination. Part 12: Bromination of 7-oxabenzonorbornadiene: Synthesis of 2,3-dibromo-7-oxabenzonorbornadiene

The electrophilic addition of bromine to 7-oxabenzonorbornadiene (8) at 0 d egrees C led in high yield to the formation of dibromoaldehyde 10. However, high-temperature bromination of 8 in carbontetrachloride at 77 degrees C g ave non-rearranged products 17 and 18. From the elimination of non-rearrang ed products, 2-bromo-7-oxabenzonorbornadiene (12) was obtained. Similarly, bromination of monobromide 12 at 77 degrees C yielded the non-rearranged tr ibromides 19 and 20 while bromination of 12 at 0 degrees C gave the rearran ged product 11. The dehydrobromination of tribromides (19, 20) provided the 2,3-dibromo-7-oxabenzonorbornadiene (21), which is a synthon for the trime rization, in high yield (C) 2000 Elsevier Science Ltd. All rights reserved.