The addition of benzyne to benzofuran. A ready route to Benz[e]acephenanthrylene

Abstract

The title reaction affords the 2+2 cycloadduct cis-4b,9b-dihydrobenzo[3,4]cyclobuta[1,2-b]benzofuran (13) together with the bis-adduct (4aα,8bα,9β,13b β)-8b,9-dihydro-9,13b-epoxy-13bH- benzo[3,4]cyclobuta[l,2-k]phenanthrene (14) in a ratio of c. 1 : 8. The mechanism of formation of these adducts is suggested to occur through a non-concerted pathway. Treatment of (14) with acid results in rearrangement and dehydration to give benz[e]acephenanthrylene in good yield.