Analysis of Cyclohexa-1,4-dienes with an Asymmetrically Substituted, 3° Carbon Atom as Chiral Dihydrogen Surrogates in Reagent-Controlled Transfer Hydrogenation of Alkenes.

Building on a reagent-controlled, trityl-cation-initiated enantioselective transfer hydrogenation of alkenes recently developed by us, a broad set of chiral cyclohexa-1,4-diene-based dihydrogen surrogates was synthesized and applied to the reduction of 1,1-disubstituted alkenes. The expanded structural diversity allowed for a more refined investigation of the structure-selectivity relationship. The experimental results are in agreement with earlier computational predictions and highlight the role of steric factors proximal (gray circle) and distal (black circle) to the stereocenter in governing the efficiency of transfer hydrogenation.