Friedel‐Crafts alkylation of pyrene in carbon disulfide; 1H NMR spectroscopy of pyrene derivatives

Abstract Friedel‐Crafts alkylation of pyrene with 2,5‐dichloro‐2,5‐dimethylhexane and 2,4‐dichloro‐2,4‐dimethylpentane in carbon disulfide yields 7,7,10,10‐tetramethyl‐7,8,9,10‐tetrahydrobenzo[ a ]pyrene and 7J,9,9‐tetramethyl‐8,9‐dihydro‐7 H ‐cyclopenta[ a ]pyrene, respectively, both in 99% yield. Alkylation with 1,4‐dichlorobutane, followed by aromatization, yields benzo[ a ]pyrene in a facile two‐step synthesis in 8% yield. A mechanism is proposed which rationalizes the fact that only one ring of pyrene undergoes substitution. The 1 H‐ 1 H NMR coupling constants of the pyrene derivatives are discussed.