Fused Ring Construction around Pyrrole, Indole, and Related Compounds via Palladium-Catalyzed Oxidative Coupling with Alkynes

Abstract

The selective synthesis of 1,2,3,4-tetrasubstituted carbazoles can be performed effectively through the palladium-catalyzed oxidative coupling reactions of N-substituted indoles or their carboxylic acid derivatives with alkynes. Unsymmetrically octasubstituted carbazoles can also be obtained by the stepwise couplings of 1-methylpyrrole-2-carboxylic acid with two different alkynes. In addition, the present coupling procedure is applicable to the synthesis of other various heteroarenes possessing di-, tri-, and tetracyclic cores. Some of the products exhibit intense fluorescence in the solid state.

Palladium-catalyzed oxidative annulation of in situ generated enones to pyrroles: a concise route to functionalized indoles

“…Palladium-catalyzed oxidative decarboxylative annulation of Nmethylpyrrole-2-carboxylic acid with alkynes generated indoles as the reaction intermediates. 10 Substituted indoles were also 35 obtained from a one-pot, two-step reactions of pyrroles with βnitroacrylates. 11 Benzannulation of pyrroles with rhodium enalcarbenoids formed substituted indoles.…”

Dehydrogenative Heck Annelations of Internal Alkynes

“…32 According to the authors, the initial step of the coupling occurs at the 3-position of the indole. Such a C-H activation is in agreement with the DHR of 1-methylindole with α,β-unsaturated esters.…”

“…32 In contrast, Jiao's experimental conditions were suitable for 3-phenylbenzofuran (Equation 20) and 2,2′-bibenzofuran (Equation 21). 36…”

“…32 Given the DHR of this substrate with alkenes, 7,37 the formation of the initial carbon-carbon bond would arise at the level of the five-membered heterocycle.…”

A Versatile Catalyst for Intermolecular Direct Arylation of Indoles with Benzoic Acids as Arylating Reagents

“…Seminal work by Miura et al on coupling reaction of benzoic acids with alkynes for construction of fused-rings implied that ortho-C À H functionalization and decarboxylative cross-coupling sequences would allow the use of benzoic acids as starting materials for the synthesis of complex molecules. [10] The high availability of benzoic acids renders these transformations very attractive.…”