NHC–AuCl/Selectfluor: An Efficient Catalytic System for π-Bond Activation

Abstract

Gold complexes have emerged as one of the most efficient catalysts for electrophilic activation of π bonds toward a variety of nucleophiles. N-Heterocyclic carbenes (NHCs), commonly described as excellent σ donors, are becoming increasingly employed in gold catalysis. Selectfluor as external oxidant is able to oxidize Au(I) to Au(III) species, which plays a unique role in the NHC-AuCl/Selectfluor combination. This account describes our recent discovery and development of this efficient catalytic system, NHC-AuCl/Selectfluor, which can be used in cross-coupling reactions of alkenes and arylboronic acids, tandem Diels-Alder/Diels-Alder (DA/DA) reactions of enynals/enynones with alkenes, and carbene-transfer reactions. We believe this account not only should help the understanding of the Au(I)/Selectfluor catalytic system but also promote the development and application of other combinations of low-oxidation-state transition metal/Selectfluor or transition metal/oxidant as catalysts in organic synthesis. 1 Introduction 2 Discovery of the NHC-AuCl/Selectfluor Catalytic System 3 Development of NHC-AuCl/Selectfluor in Tandem DA/DA Reactions of Enynals/Enynones with Alkenes 3.1 Two-Component Three-Molecule Tandem DA/DA Reactions 3.2 Three-Component Three-Molecule Tandem DA/DA Reactions 3.3 Bioinspired Intramolecular DA/DA Reactions 3.4 Investigations of Reaction Mechanism 4.