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Iridium‐Catalyzed Asymmetric Hydrogenation of Unfunctionalized, Trialkyl‐Substituted Olefins
Author(s) -
Wang Aie,
Fraga Rui P. A.,
Hörmann Esther,
Pfaltz Andreas
Publication year - 2011
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201000595
Subject(s) - enantioselective synthesis , chemistry , iridium , asymmetric hydrogenation , catalysis , organic chemistry , allylic rearrangement , pyridine , noyori asymmetric hydrogenation , enantiomer , medicinal chemistry
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 CC 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.