Exploring Gold Catalysis in a 1,6-Conjugate Addition/Domino Electrophilic Cyclization Cascade: Synthesis of Cyclohepta[b]indoles

Abstract

An effective method for the construction of the structurally complex fused cyclohepta[ b]indole core has been developed through an intermolecular 1,6-conjugate addition of indoles to 2-alkynyl p-quinone methides followed by an intramolecular electrophilic cyclization under oxophilic and alkynophilic gold catalysis.

Base-Mediated One-pot Synthesis of Oxygen-Based Heterocycles from 2-Hydroxyphenyl-Substituted para-Quinone Methides

“…In line with this, we have recently reported a one-pot protocol to access 2,3-diaryl-substituted benzo­[ b ]­furan derivatives through N -heterocyclic carbene-catalyzed 1,6-conjugate addition of aryl aldehydes to 2-hydroxyphenyl-substituted p -quinone methides followed by acid-mediated dehydrative cyclization . In continuation with our ongoing research in the area of para -quinone methides ( p -QMs), herein, we disclose an efficient one-pot method for the synthesis of 2,3-dihydrobenzofurans through base-mediated O -alkylation of 2-hydroxyphenyl-substituted p -quinone methides with α-halo ketones followed by the intramolecular 1,6-conjugate addition strategy (Scheme ). This method was also elaborated for the synthesis of 2,3-disubstituted benzo­[ b ]­furan derivatives through the in situ oxidation of 2,3-dihydrobenzofurans.…”

An Update on Cyclohepta[b]indoles

“…p-quinone methides 74 (Figure 24). [35] The method could be useful in accessing rather exotic cyclohepta[b]indole-based azaacenes.…”

“…reported the synthesis of cyclohepta[ b ]indole‐derived tetra‐ and pentacycles 75 by Au‐catalyzed intermolecular (5+2) cycloaddition of indoles 73 and 2‐alkynyl p ‐quinone methides 74 (Figure 24). [35] The method could be useful in accessing rather exotic cyclohepta[ b ]indole‐based azaacenes.…”

Advances in The Catalytic Synthesis of Triarylmethanes (TRAMs)

“…A similar strategy was devised by Anand and co‐workers for the construction of fused cyclohepta[b]indole core by installing an alkynyl moiety adjacent to the para ‐quinonemethide linkage. The fused cyclohepta[b]indole core 103 was realized by an intermolecular 1,6‐conjugate addition of nucleophilic indole 22 to 2‐alkynyl para ‐quinonemethides 102 followed by AgOTf/PPh 3 AuCl catalyzed electrophilic cyclization at room temperature (Scheme ) …”