PdII-Catalysed CH Functionalisation of Indoles and Pyrroles Assisted by the Removable N-(2-Pyridyl)sulfonyl Group: C2-Alkenylation and Dehydrogenative Homocoupling

✍ Scribed by Alfonso García-Rubia; Beatriz Urones; Ramón Gómez Arrayás; Juan Carlos Carretero

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 402 KB
• Volume: 16
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.201001126

✦ Synopsis

Abstract

The easily installed and removed N‐(2‐pyridyl)sulfonyl group exerts complete C2 regiocontrol over the Pd^II^‐catalysed CH alkenylation of indoles and pyrroles, affording the corresponding products in good isolated yields (typically ≥70 %). A remarkable feature of this catalyst system is that it tolerates a wide variety of substituted alkenes, including conjugated electron‐deficient alkenes, styrenes and 1,3‐dienes, as well as conjugated 1,1‐ and 1,2‐disubstituted olefins. The final reductive desulfonylation affords the C2‐substituted, free‐NH indoles and pyrroles in good yield. This N‐(2‐pyridyl)sulfonyl‐directing strategy has also been extended to the development of a protocol for the intermolecular, dehydrogenative homocoupling of indoles, providing 2,2′‐biindoles. Mechanistic work based upon reactions with isotopically labelled starting materials and competitive kinetic studies of electronically varied substrates suggests a chelation‐assisted electrophilic aromatic substitution palladation mechanism.