Palladium(II)-Catalyzed Intramolecular [2 + 2 + 2] Annulation of Indolyl 1,3-Diynes: Construction of Azepino-Fused Carbazoles

Abstract

A novel palladium­(II)-catalyzed intramolecular [2 + 2 + 2] annulation of indolyl 1,3-diynes is described in this contribution. A variety of azepino-fused carbazoles are obtained in moderate to excellent yields. The key to the success of this transformation is the use of a carboxylic acid as an additive. This protocol features broad functional group tolerances, easy handling in air, and 100% atom economy. Furthermore, scale-up reactions, late-stage derivatizations, and photophysical property investigations highlight the potential synthetic utility of this methodology.

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part C: The Domino Diarylation and Annelation Reactions

“…[25] A recent report disclosed the Pd II -catalyzed intramolecular [2 + 2 + 2] annelation of indolyl 1,3diyne 8 a leading to azepino-fused carbazole 8a1 in yield improved from 29% under carboxylic acidfree conditions to 75% in the presence of benzoic acid, acetic and propargylic acids being less efficient (Scheme 8a). [27] According to Wu, Yang and co-workers, coordination of the internal triple bond of 8 a to a cationic Pd II complex promotes 7exo-dig cyclization giving 8bA (Scheme 8b). Protonolysis of the latter provides 8bB which undergoes 6-endo-dig cyclization giving 8bC.…”

Development of 3-triazenylaryne and its application to iterative aryne reactions via o-triazenylarylboronic acids

“…Reportedly, 1,3-diyne moieties are convertible into various five- or six-membered hetero- and carbo-cycles. 19 Indeed, iodoalkynylation product 7e was converted into thiophene 9 via treatment with Na 2 S·9H 2 O. 19 b This result demonstrates the potential accessibility of arynes conjugated with a range of heteroaromatic moieties through the reaction of 3-triazenylaryne with 1,3-diynes.…”

Cascade hydroarylation/Diels–Alder cycloaddition of alkynylindoles with electron-deficient alkynes and alkenes

“…As part of our ongoing interest in indole chemistry, 11 we have already described several interesting investigations from indole substrates to construct polycyclic indole skeletons. Based on these findings contributed by us and others, 12 we postulated that indole A bearing a remote terminal alkyne might undergo gold( i )-catalyzed hydroarylation 13 to afford the trans -alkenyl gold complex C through selectively 7- exo-dig cyclization 14 of B , which then undergoes protonation of the alkenyl–gold intermediate to form the azepino-fused 2-vinylindole D .…”