A facile synthesis of pyrrolo[2,3‐j]phenanthridines via the cascade reaction of indoleanilines and aldehydes

Abstract

A facile method for the synthesis of pyrrolo[2,3‐j]phenanthridines from indoleanilines and aldehydes in the presence of Brønsted acid catalyst and benzoquinone oxidant has been established. This approach features excellent yields, high efficiency and a wide range of substrate scope. Mechanism studies exhibited that this reaction was a cascade process including acid‐catalyzed condensation of indoleanilines with aldehydes, cyclization and oxidative aromatization.

Brønsted acid-catalyzed C6 functionalization of 2,3-disubstituted indoles for construction of cyano-substituted all-carbon quaternary centers

“…7–11 The approaches to generate δ , δ -disubstituted p -QMs include Brønsted acid-catalyzed dehydration of p -hydroxybenzyl alcohols 8,9 and oxidant mediated C–H oxidation of diarylmethanes bearing electron-withdrawing groups. 10,11 b Owing to our interest in C6 functionalization of 2,3-disubstituted indoles, 3 d ,12 we conceived the catalytic direct C6 functionalization of 2,3-disubstituted indoles with δ , δ -disubstituted p -QMs which were in situ generated from 2,2-diarylacetonitriles under oxidative conditions. The electron-withdrawing cyano group of 2,2-diarylacetonitrile would tune the molecular electron-density distribution, and the stability of the resulting p -QMs might be enhanced by reducing their polymerizability.…”

Efficient synthesis of new 6-arylphenanthridines based on microwave-assisted Suzuki–Miyaura cross-coupling and Pictet–Spengler dehydrogenative cyclization in a zinc chloride/[Bmim]BF4 mixture

“…According to the reported methods, the construction of a phenanthridine core is achieved through the following synthetic models (Fig. 2): (1) C Ar –C Ar bond formation via intramolecular cyclization of functionalized imines or anilines or by transition-metal-catalysed coupling of ortho -halogenated amines/imines with aryl halides or triflates 12,13 (model 1); (2) C Ar –N bond formation of the respective ortho -biaryl keto and aldoximes 14–17 (model 2); and (3) C–C bond formation through intramolecular cyclization of ortho -aryl isocyanides 18–20 or C Ar –C ymine bond formation through intramolecular cyclization of ortho -arylimines (amines, imines or amides) 21–26 (model 3). The latter disconnection type includes the well-known Bischler–Napieralski and Pictet–Hubert type cyclization reactions, which are primary methods for phenanthridine preparation using N -acylbiphenyl-2-amine derivatives.…”