Room Temperature Palladium-Catalyzed 2-Arylation of Indoles

Abstract

This communication describes the rational development of a PdII-catalyzed method for the direct 2-arylation of indoles using [Ar-IIII-Ar]BF4. These reactions proceed under remarkably mild conditions (often at room temperature and in the presence of ambient air and moisture), and these features are believed to be the result of a PdII/IV mechanism operating in these systems. These transformations can be used to prepare functionally diverse 2-arylated indoles and pyrroles, and their potential utility has been expanded by the development of an in situ procedure for generating the iodine(III) arylating reagents.

C-2/C-3 Annulation and C-2 Alkylation of Indoles with 2-Alkoxycyclopropanoate Esters

“…Recent examples of indole functionalization include asymmetric C-3 Friedel-Craft reactions, 1,2,3 allylations, 4,5 radical couplings, 6 arylations, 7,8,9 Michael-additions, 10 C-H activation, 11 and N-arylations. 12 Indoles containing a fused 5-membered ring at the C-2 and C-3 positions are well represented in nature, and include the penitrems 13 and kopsane 14 alkaloids.…”

Diaryliodonium Salts in Organic Syntheses: A Useful Compound Class for Novel Arylation Strategies

“…81 They utilized symmetric diaryliodonium salts as powerful arylating agents. In most cases, the arylation can be performed at room temperature, in acetic acid as a solvent.…”

Catalytic Direct Arylation of Heteroaromatic Compounds

“…The 2-arylation of indole itself occurs under rhodium catal- 10 The palladium-catalyzed 2-arylation of N-protected indoles as well as pyrroles with aryl iodides has been described.…”