Counter Ion Effect in Au/Ag-Catalyzed Chemoselective 6-endo-dig N‑ and O‑Cyclizations of Enyne–Urea System: Diversity-Oriented Synthesis of Annulated Indoles

A two-step protocol for the diversity-oriented synthesis of annulated indoles following MCR-post MCR modification concept is described. The reaction initially proceeds through the annulation of 2-(2,2-dibromovinyl)aniline, an isocyanate, and a terminal alkyne in a three-component tandem format via C...

Full description

Saved in:
Bibliographic Details
Published in:Journal of organic chemistry 2013-09, Vol.78 (17), p.8624-8633
Main Authors: Gupta, Sahaj, Koley, Dipankar, Ravikumar, Krishnan, Kundu, Bijoy
Format: Article
Language:English
Subjects:
Alkynes - chemistry
Catalysis
Cyclization
Gold - chemistry
Indoles - chemical synthesis
Indoles - chemistry
Molecular Structure
Silver - chemistry
Urea - chemistry
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:A two-step protocol for the diversity-oriented synthesis of annulated indoles following MCR-post MCR modification concept is described. The reaction initially proceeds through the annulation of 2-(2,2-dibromovinyl)aniline, an isocyanate, and a terminal alkyne in a three-component tandem format via Cu/Pd-catalyzed cross coupling to afford N-1 and C-2 functionalized indole. In the subsequent step, the enyne–urea derivative undergoes chemo- and regioselective 6-endo cyclization to afford O-cyclized product in the presence of Au(I)/AgNO3 and N-cyclized product in the presence of Au(I)/AgOTf under a post-MCR modification step. A mechanistic investigation following a recent pioneering work on the silver effect in gold catalysis ( Shi X. J. Am. Chem. Soc. 2012, 134, 9012 ) explains the role of counterion on Au/Ag-catalyzed regiodivergent pathways.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo4013332