The monomethyl and dimethyl derivatives of benzo[e]pyrene

Convenient syntheses of the previously unknown complete set of six isomeric monomethyl derivatives of benzoe]pyrene, 1-, 2-, 3-, 4-, 9- and 10-methylbenzoe]pyrene, are described. Syntheses of 1-, 2- and 3-methylbenzoe]pyrene were accomplished through reaction of 7H-benzanthrene (or its 1-Me derivative as appropriate) with 1, 3-bis(dimethylamino)trimethinium perchlorate (or its 1-Me derivative) followed by thermal electrocyclic ring closure accompanied by elimination and aromatization. The earlier claim¹⁶ that the analogous isomeric benzoa]pyrene derivatives are principal products of reactions of this type is disproven. Synthesis of 3,6- and 4,5-dimethylbenzoe]pyrene are also described. The structural assignments of all mono- and dimethyl benzoe] pyrene products are supported by high resolution 270 MHz proton NMR spectra; the chemical shifts and coupling constants of all aromatic protons are fully assigned.