Scope and mechanism of the Pd(II)-catalyzed arylation/carboalkoxylation of unactivated olefins with indoles.

Published

Journal Article

Treatment of 1-methyl-2-(4-pentenyl)indole (5) with a catalytic amount of [PdCl2(MeCN)2] (2; 5 mol %) and a stoichiometric amount of CuCl2 (3 equiv) in methanol under CO (1 atm) at room temperature for 30 min gives methyl (9-methyl-2,3,4,9-tetrahydro-4-carbazolyl)acetate (6), which was isolated in 83% yield. A number of 2- and 3-alkenyl indoles undergo a similar palladium-catalyzed cyclization/carboalkoxylation to give the corresponding polycyclic indole derivatives in moderate to excellent yields with excellent regio- and diastereoselectivity. Under similar conditions, vinyl arenes undergo intermolecular arylation/carboalkoxylation with indoles to give 3-(1-aryl-2-carbomethoxyethyl) indoles in moderate yield with high regioselectivity. Stereochemical analyses of the palladium-catalyzed cyclization/carboalkoxylation of both 2- and 3-alkenyl indoles are in agreement with mechanisms involving outer-sphere attack of the indole on a palladium-olefin complex followed by alpha-migratory insertion of CO and methanolysis of the resulting acyl palladium intermediate. CuCl2 functions as the terminal oxidant in this palladium-catalyzed cyclization/carboalkoxylation of alkenyl indoles and also significantly increases the rate of reaction of 2 with the alkenyl indole to form the corresponding acyl palladium complex. Spectroscopic studies are in agreement with the intermediacy of a heterobimetallic Pd/Cu complex as the active catalyst in this reaction.

Full Text

Duke Authors

Cited Authors

  • Liu, C; Widenhoefer, RA

Published Date

  • March 2006

Published In

Volume / Issue

  • 12 / 8

Start / End Page

  • 2371 - 2382

PubMed ID

  • 16416492

Pubmed Central ID

  • 16416492

Electronic International Standard Serial Number (EISSN)

  • 1521-3765

International Standard Serial Number (ISSN)

  • 0947-6539

Digital Object Identifier (DOI)

  • 10.1002/chem.200500787

Language

  • eng