A RAPID, CONVERGENT, AND REGIOSELECTIVE SYNTHESIS OF ANTHRACENES

Anthracenes are obtained in moderate to good yield by the simultaneous treatment of benzocyclobutenols and halobenzenes with LTMP in tetrahydropyran. In the key step of this one-pot process, o-toluoyl anion intermediates from the known ring-opening of benzocyclobutenoxides add to halobenzene derived arynes. Methoxy-substituted benzocyclobutenols which are readily made regiospecifically by known methods also react regiospecifically with the single benzyne generated from either a 2- or 3-haloanisole. For example, the only trimethoxyanthracene isolated (48% yield) from the reaction of 6-methoxybenzocyclobutenol (8) with 5-chloro-1,3-dimethoxybenzene is the 1,3,8-isomer 20. When 1,2-dihydrocyclobuta[l]phenanthren-1-ol (14) and/or halonaphthalenes are the reactants, benzannulated anthracenes are formed; e.g., tribenz[a,c,h]anthracene in 68% yield from 14 and bromonaphthalene. In another extension, pentaphene (31) was made in one pot from o-dichlorobenzene.