Acid-catalyzed Dimerization Reaction of Pyrroles to Synthesize Hexaaryl-4,8-dihydropyrrolo[2,3-f]indoles

Abstract

Pyrroloindoles, as a kind of promising small-melecular hole injetion materials, have attracted wide attention. Herein, we described a simple metal-free method for the synthesis of 4,8-dihydropyrrolo[2,3-f]indole compounds through the acid-catalyzed dimerization reaction of pyrroles. The structures of target 4,8-dihydropyrrolo-[2,3-f]indoles were confirmed by NMR spectrum and X-ray single crystal diffraction. Notably, pyrrole substrates were synthesized conveniently starting from available biological dipeptides. cis-Configuration was preferred when bulky p-toluene sulfonic acid(TsOH) was employed. Excessive aicds empoyed in dimerization would lead to the formation of quantitative pyrrolium chloride intermediate, restraining further conversion to target compounds. Furthermore, the dimerization process was monitored by ¹H NMR spectrum, proving that it followed a second-order kinetics, providing significant insight to the mechanism of dimerization reaction.

Keywords

Dimerazation / Pyrroloindole / Benzoheterole / Pyrrole

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