Well‐defined NHCPd complex‐mediated intermolecular direct annulations for synthesis of functionalized indoles (NHC = N‐hetero‐cyclic carbene)

Abstract

AbstractAs alternatives to the common tertiary phosphine/Pd systems, well‐defined N‐heterocyclic carbene–Pd complexes have been proven to be highly efficient precatalysts for intermolecular direct annalution of o‐haloanilines and ketones at lower catalyst loadings. A highly efficient and practical protocol for synthesis of functionalized indoles was developed using (IPr)Pd(acac)Cl as catalyst. Both o‐bromoanilines and o‐chloroanilines gave rise to efficient coupling under the reaction conditions. Related to acyclic ones, cyclic ketones coupled more effectively with o‐haloanilines. With [Pd(IPr)2] as catalyst, the base‐sensitive groups including OH and CO2H groups could be tolerated. Copyright © 2011 John Wiley & Sons, Ltd.