Add time:07/17/2019         Source:sciencedirect.com

Convenient syntheses of the previously unknown complete set of six isomeric monomethyl derivatives of benzo[e]pyrene, 1-, 2-, 3-, 4-, 9- and 10-methylbenzo[e]pyrene, are described. Syntheses of 1-, 2- and 3-methylbenzo[e]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 benzo[a]pyrene derivatives are principal products of reactions of this type is disproven. Synthesis of 3,6- and 4,5-dimethylbenzo[e]pyrene are also described. The structural assignments of all mono- and dimethyl benzo[e] 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.

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