Access to 5H-benzo[a]carbazol-6-ols and benzo[6,7]cyclohepta[1,2-b]indol-6-ols via rhodium-catalyzed C–H activation/carbenoid insertion/aldol-type cyclization

Abstract

The rhodium-catalyzed mono-ortho C–H activation/carbenoid insertion/aldol-type cyclization of 3-aldehyde-2-phenyl-1H-indoles with diazo compounds has been developed.

The solvent-controlled Rh(iii)-catalyzed switchable [4+2] annulation of 2-arylIndoles with iodonium ylides

“…Based on the above results and literature precedence, 6,13 a plausible mechanism was proposed, as shown in Scheme 4. First, according to the proposed mechanism, the catalytic cycle is initiated by forming an active catalyst- A as a result of ligand exchange with CsOAc.…”

“…5 In contrast to these landmark reports, Fan et al developed a Rh( iii )-catalyzed C–H activation and subsequent annulation of 2-arylindoles with carbene precursors to access the benzo[ a ]carbazoles exclusively (Scheme 1b). 6 Intriguingly, 2-arylindole has become an attractive directing group in C–H functionalizations—and, when coupled with diverse precursors such as alkenes, quinones, and maleimides, has been investigated for the construction of various indole-containing polycyclic scaffolds. 7…”

An Update on Cyclohepta[b]indoles

“…(Figure 27). [37] In 2021, Yang et al reported the synthesis of substituted hexahydrocyclohepta[b]indoles 85 by photocatalyzed cyclization of tryptamine-derived vinylogous amides 83 (Figure 28). [38] The Ir(III) complex 84 served as the photocatalyst and operated under irradiation with visible light.…”

Rhodium-Catalyzed Oxidative Annulation of 2- or 7-Arylindoles with Alkenes/Alkynes Using Molecular Oxygen as the Sole Oxidant Enabled by Quaternary Ammonium Salt

“…Since then, rhodium-catalyzed oxidative C-H coupling has drawn increasing attention, and many important organic building blocks have been produced [23][24][25][26][27][28][29][30]. However, despite indisputable advances, all rhodium-catalyzed C-H oxidative coupling reactions are extremely limited to hazardous and stoichiometric oxidants such as AgOAc [31][32][33][34][35][36][37] and Cu(OAc) 2 [38][39][40][41][42][43][44][45][46][47]. The use of molecular oxygen is advantageous over other oxidants because only water is generated as a by-product [48][49][50][51][52][53][54].…”