Copper (II) as catalyst for intramolecular cyclization and oxidation of (1,4-phenylene)bisguanidines to benzodiimidazole-diylidenes

• Published in: Journal of catalysis 2020-02, Vol.382, p.150-154
• Main Authors: Mesias-Salazar, Angela, Trofymchuk, Oleksandra S., Daniliuc, Constantin G., Antiñolo, Antonio, Carrillo-Hermosilla, Fernando, Nachtigall, Fabiane M., Santos, Leonardo S., Rojas, René S.
• Format: Article
• Language: English
• Subjects: Catalysis; Copper acetate; Cyclization; ESI-MS; Guanidines
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2019.12.002

[Display omitted] •Catalytic cyclization of guanidines was studied by on line monitoring of the reaction by ESI-MS.•All-important intermediates organic species were intercepted during the experiment.•The key copper-containing intermediate was intercepted and characterized.•The plausible key mechanistic steps are presented. A synthetically useful approach of catalytic intramolecular cyclization and oxidation of 2′,2′-(1,4-phenylene)bis(1,3-dialkyl)guanidines (Alkyl = isopropyl 1 or cyclohexyl 2) catalyzed by copper acetate in acetonitrile under air was studied by on line monitoring of the reaction by ESI-MS. All-important intermediates organic species were intercepted during the experiment confirming for the first time the stepwise (1,4-phenylene)bisguanidines cyclization and oxidation mechanism. Moreover, performed collision-induced dissociation (CID) experiments were also applied as a structure elucidation tool. Bimetallic copper intermediates Cu1 ([C28H48Cu2N6O10 + H]+) of m/z 755 and Cu2 [C22H36Cu2N6O4 + H]+ of m/z 575 were documented. The plausible key mechanistic steps involving the formation of organic and inorganic intermediates detected by in situ monitoring of the reaction are presented.