Highly Enantioselective Borane Reduction of Heteroaryl and Heterocyclic Ketoxime Ethers Catalyzed by Novel Spiroborate Ester Derived from Diphenylvalinol: Application to the Synthesis of Nicotine Analogues
journal contributionposted on 2008-06-06, 00:00 authored by Kun Huang, Francisco G. Merced, Margarita Ortiz-Marciales, Héctor J. Meléndez, Wildeliz Correa, Melvin De Jesús
An asymmetric synthesis for the preparation of nonracemic amines bearing heterocyclic and heteroaromatic rings is described. A variety of important enantiopure thionyl and arylalkyl primary amines were afforded by the borane-mediated enantioselective reduction of O-benzyl ketoximes using 10% of catalyst 10 derived from (S)-diphenylvalinol and ethylene glycol with excellent enantioselectivity, in up to 99% ee. The optimal condition for the first asymmetric reduction of 3- and 4-pyridyl-derived O-benzyl ketoxime ethers was achieved using 30% of catalytic loading in dioxane at 10 °C. (S)-N-ethylnornicotine (3) was also successfully synthesized from the TIPS-protected (S)-2-amino-2-pyridylethanol in 97% ee.
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enantioselectivitydioxaneheteroaromatic ringscatalyst 10eeNicotine AnaloguesApplicationDiphenylvalinolethylene glycoletherarylalkylenantioselectivevarietyHeteroarylnonracemic aminessynthesisEnantioselective Borane Reductionenantiopure thionylketoximeNovel Spiroborate Ester DerivedHeterocyclic Ketoxime Ethers CatalyzedheterocyclicpreparationloadingSynthesi