Abstract
Thioethers allowed for highly atroposelective C–H olefinations by a palladium/chiral phosphoric acid catalytic system under ambient air. Both N–C and C–C axial chiral (hetero)biaryls were successfully constructed, leading to a broad range of axially chiral N-aryl indoles and biaryls with excellent enantioselectivities up to 99% ee. Experimental and computational studies were conducted to unravel the walking mode for the atroposelective C–H olefination. A plausible chiral induction model for the enantioselectivity-determining step was established by detailed DFT calculations.
Highlights
Chiral compounds are ubiquitous structural motifs in biologically active natural products,[1] privileged catalysts,[2] chiral ligands[3] and material sciences.[4]
Isoquinolines and pyridines were employed in rhodium-catalyzed C–H functionalization for axially chiral biaryl compounds synthesis by Murai,[9] You,10a and Lassaletta.[11]
Pyridine N-oxides were applied to palladium-catalyzed asymmetric C–H iodination by You.10b Chiral sulfoxides as directing groups (DGs) were elegantly utilized for diastereoselective C–H activation by Wencel-Delord/Colobert.[12]
Summary
Chiral compounds are ubiquitous structural motifs in biologically active natural products,[1] privileged catalysts,[2] chiral ligands[3] and material sciences.[4]. Scheme 1 Atroposelective C–H activation for axial chirality. Salient features of our ndings include (a) thioetherdirected atroposelective C–H functionalization, (b) construction of N–C axially chiral scaffolds in the absence of toxic oxidants, and (c) key mechanistic insights into the mode of enantio-induction by DFT calculations.
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