The Chemistry of Phenalenium Systems. XXXI. The Synthesis, Dimerization, and Trapping of 6-Methylenebenzo[cd]pyrene

Abstract

Abstract The acetolysis of 6-mesyloxymethyl-6H-benzo[cd]pyrene (6) gave 7,7a-dihydrospiro[benzo[ghi]perylene-5-(6H),6′-[6H]benzo[cd]pyrene] (13), whereas, on formolysis, 6 gave spiro[benzo[ghi]perylene-5(6H),6′-[6H]benzo[cd]-pyrene], 6-hydroxymethyl-6H-benzo[cd]pyrene, and 6-methyl-6H-benzo[cd]pyrene as well as 13. It might reasonably be supposed that the formation of 13 proceeds in a process involving four steps: (i) the formation of the intermediate 6H-6-benzo[cd]pyren-6-ylmethyl cation (8); (ii) the conversion of 8 into the reactive 6-methylenebenzo[cd]pyrene (5) by the loss of a proton; (iii) the head-to-head self-Diels-Alder dimerization of 5 to the initial dimer, 6,7-dihydrospiro[benzo[ghi]perylene-5(4aH),6′-[cd]benzo[cd]pyrene], and (iv) a 1,3-hydrogen shift to form 13. When 6-methylbenzo[cd]pyren-6-yl tetrafluoroborate (7) was treated with triethylamine in chloroform, the spiro-dimer, 13, was also obtained. The reaction of 7 with triethylamine in the presence of dimethyl acetylenedicarboxylate resulted in the formation of dimethyl benzo[ghi]perylene-5,6-dicarboxylate. These results strongly suggest the intermediate formation of 5 as a reactive compound.