Structural Features and Asymmetric Environment of i‐Pr‐SPRIX Ligand

Abstract

Novel chiral diisopropyl spiro bis(isoxazoline) ligands, anti-i-Pr-SPRIX and syn-i-Pr-SPRIX, were designed and synthesized. Their catalytic utility, X-ray crystallographic analyses, and complexation studies demonstrated the structural features of tetraisopropyl spiro bis(isoxazoline) ligand, i-Pr-SPRIX, which is a prominent ligand in various enantioselective Pd catalytic processes: All i-Pr groups work in collaboration to create an effective asymmetric environment.

Enantioselective Palladium-Catalyzed Oxidative Cascade Cyclization of Aliphatic Alkenyl Amides

“…Compared to acrylanilides with fused aryl backbones, aliphatic acrylamides possess less rigid skeletons and less acidic NH and are thus unfavorable for the desired cyclization. As reported by Sasai and co-workers, low to moderate enantioselectivity (up to 61% ee) was observed on cyclization of such acrylamides substrates with the Pd­(II)/spirobis­(isoxazoline) (SPRIX) (Scheme , eq 2) system, which previously exhibited excellent enantiocontrol in C–C, C–O, as well as C–N bond formation. We herein describe a highly enantioselective oxidative tandem cyclization of alkene-tethered aliphatic acrylamides catalyzed by Pd­(TFA) 2 /( S , S )-diPh-pyrox that affords a series of pyrrolizidines in excellent yield (up to 99%) and enantioselectivity (up to 93% ee) (Scheme , eq 3) under mild conditions.…”