NHC–Au(I) catalyzed enantioselective intramolecular [4+3] cycloaddition of furan propargyl esters

Abstract

Enantioselectivity up to 75% ee has been achieved for an intramolecular [4 + 3] cycloaddition reaction with a series of chiral gold(I) complexes. Nine new chiral NHC–Au(I) complexes featuring disilylbiphenyl derived chiral N-heterocyclic carbene ligands were synthesized and identified by 1H, 13C NMR spectroscopy and X-ray single crystal structure analysis. The corresponding activated Au(I) catalysts with a phenyl nitrile dynamic ligand were prepared and used in the catalysis of intramolecular [4 + 3] cycloaddition reactions. Moderate to high chemical yields and enantioselectivity were achieved with 5% mol of the chiral NHC–Au(I) catalysts. The stereochemistry of the intramolecular [4 + 3] cycloaddition product was identified by X-ray single crystal structure analysis. The absolute configuration of the cycloaddition products was deduced by a combination of X-ray single crystal structure analysis, NMR and DFT study.