Combinatorial Ligand Assisted Simultaneous Control of Axial and Central Chirality in Highly Stereoselective C-H Allylation

The significance of stereoselective C-H bond functionalization thrives on its direct application potential to pharmaceuticals or complex chiral molecule synthesis. Complication arises when there are multiple stereogenic elements such as a center and an axis of chirality to control. Over the years cooperative assistance of multiple chiral ligands has been applied to control only chiral centers. In this work, we harness the essence of cooperative ligand approach to control two different stereogenic elements in the same molecule by atroposelective allylation to synthesize axially chiral biaryls from its racemic precursor. The crucial roles played by chiral phosphoric acid and chiral amino acid ligand in concert helped us to obtain one major stereoisomer out of four distinct possibilities. The aim of converging multiple stereocenters in asymmetric catalysis brings exciting avenues for expanding the 'chiral pool'. With this aim, a dual-cooperative ligand system was developed for controlling two distinct stereo-environment in an atropselective C-H allylation of biaryls. The system leverages a chiral amino acid as a transient-ligand source and chiral phosphoric acid for the early C-H activation step. The DFT studies present a rich mechanistic model, authenticating the extensive experimental findings.image