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Broad Scope Synthesis of Ester Precursors of Nonfunctionalized Chiral Alcohols Based on the Asymmetric Hydrogenation of α,β-Dialkyl-, α,β-Diaryl-, and α-Alkyl-β-aryl-vinyl Esters

AuthorsLeón, Felix; González-Liste, Pedro J.; García-Garrido, Sergio E.; Arribas, Inmaculada ; Rubio, Miguel ; Cadierno, Victorio; Pizzano, Antonio
Issue Date2017
PublisherAmerican Chemical Society
CitationJournal of Organic Chemistry 82: 5852- 5867 (2017)
AbstractThe catalytic asymmetric hydrogenation of trisubstituted enol esters using Rh catalysts bearing chiral phosphine-phosphite ligands (P-OP) has been studied. Substrates covered comprise α,β-dialkyl, α-alkyl-β-aryl, and α,β-diarylvinyl esters, the corresponding hydrogenation products being suitable precursors to prepare synthetically relevant chiral nonfunctionalized alcohols. A comparison of reactivity indicates that it decreases in the order: α,β-dialkyl > α-alkyl-β-aryl > α,β-diaryl. Based on the highly modular structure of P-OP ligands employed, catalyst screening identified highly enantioselective catalysts for α,β-dialkyl (95-99% ee) and nearly all of α-alkyl-β-aryl substrates (92-98% ee), with the exception of α-cyclohexyl-β-phenylvinyl acetate which exhibited a low enantioselectivity (47% ee). Finally, α,β-diarylvinyl substrates showed somewhat lower enantioselectivities (79-92% ee). In addition, some of the catalysts provided a high enantioselectivity in the hydrogenation of E/Z mixtures (ca. Z/E = 75:25) of α,β-dialkylvinyl substrates, while a dramatic decrease on enantioselectivity was observed in the case of α-methyl-β-anisylvinyl acetate (Z/E = 58:42). Complementary deuteration reactions are in accord with a highly enantioselective hydrogenation for both olefin isomers in the case of α,β-dialkylvinyl esters. In contrast, deuteration shows a complex behavior for α-methyl-β-anisylvinyl acetate derived from the participation of the E isomer in the reaction.
Identifiersdoi: 10.1021/acs.joc.7b00710
issn: 1520-6904
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