Remote Cooperative Group Strategy Enables Ligands for Accelerative Asymmetric Gold Catalysis

An accelerative asymmetric gold catalysis
is achieved for the first
time via chiral ligand metal cooperation. An asymmetrically positioned
remote amide group in the designed chiral binaphthyl-based ligand
plays the essential role of a general base catalyst and selectively
accelerates the cyclizations of 4-allen-1-ols into one prochiral allene
face. The reactions are mostly highly enantioselective with achiral
substrates, and due to the accelerated nature of the catalysis catalyst
loadings as low as 100 ppm are allowed. With a pre-existing chiral
center at any of the backbone sp3-carbons, the reaction
remained highly efficient and most importantly maintained excellent
allene facial selectivities regardless of the substrate stereochemistry.
By using different combinations of ligand and substrate enantiomers,
it is now possible to access all four stereoisomers of versatile 2-vinyltetrahydrofurans
with exceedingly high selectivity. The underpinning design of this
chemistry reveals a novel and conceptually distinctive strategy to
tackle challenging asymmetric gold catalysis, which to date has relied
on decelerative asymmetric steric hindrance approaches.