Iridium‐Catalyzed Asymmetric Hydrogenation of Unfunctionalized, Trialkyl‐Substituted Olefins

Abstract Chiral iridium complexes with bicyclic pyridine‐based N,P ligands have emerged as efficient catalysts for the enantioselective hydrogenation of unfunctionalized trialkyl‐substituted olefins. Optimization of the reaction conditions by variation of the solvent, pressure, and temperature led to enantiomeric excesses of up to 99 %. Three pure alkenes, ( E )‐2‐cyclohexyl‐2‐butene and ( E )‐ and ( Z )‐3,4‐dimethyl‐2‐pentene were converted into the corresponding chiral alkanes with 97 %, 94 %, and 93 % ee , respectively. Hydrogenation of the three CC bonds of both α‐ and γ‐tocotrienyl acetate led to α‐ and γ‐tocopheryl acetate with very high diastereoselectivity. The same catalysts were successfully applied in the hydrogenation of trisubstituted alkenes with a carboxylic ester or a keto group in the γ position. This reaction was used as a key step in a highly enantioselective synthesis of the pheromone of the caddisfly Hesperophylax occidentalis. The hydrogenation of a structurally analogous allylic alcohol also gave high enantioselectivities.