Enantioselective Deuteration of -Substituted ,-Unsaturated Esters by Rhodium-1,2-Bis(2,5-diphenylphospholano)ethane

We report an efficient method for the synthesis of a chiral C‐CHD‐CHD‐C unit in threo form, which enables the asymmetric conformational analysis of straight alkyl chains. The vicinal dideuterated compound was constructed by enantioselective catalytic deuteration of β‐substituted α,β‐unsaturated esters. To obtain an enantiomeric excess > 90 %, it was crucial to utilize a rhodium catalyst with 1,2‐bis(2,5‐diphenyl‐phospholano)ethane (PhBPE) ligand. The substrate was derivatized with a chiral methyl mandelate ester for the dual purposes of carboxylate protection and providing a direct read‐out of enantiomeric excess via ¹H NMR spectroscopy. Due to the steric bulk of PhBPE, enantioselectivity was controlled almost exclusively by catalyst stereochemistry, regardless of the chirality of the mandelate moiety in the substrate. The present study provides a robust method for catalytic asymmetric deuteration of β‐substituted α,β‐unsaturated esters.