An oxidation induced by potassium metal. Studies on the anionic cyclodehydrogenation of 1,1'-binaphthyl to perylene

Oxidative cyclization of 1,1'-binaphthyl (1) to perylene (2) can be achieved in essentially quantitative yield by the action of three or more equivalents of potassium metal in hot tetrahydrofuran. An overall reaction mechanism is proposed that accounts for all of the experimental observations reported by previous investigators and those from the present studies. The trans-6a,6b-dihydroperylene dianion (6(2-)) is believed to be the pivotal intermediate from which H(2) is lost. A radical chain reaction involving free hydrogen atoms (H(•)) in the two-step propagation cycle is proposed to explain the formation of H(2) from 6(2-). Anionic cyclodehydrogenations of this sort are complementary to those performed under strongly acidic/oxidizing conditions, photochemically, or thermally (flash vacuum pyrolysis), and a better understanding of how they occur, together with the optimized synthetic protocol reported here, should encourage their wider use in organic synthesis.