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
(Chemical Equation Presented) 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.
Huang, Kun,Merced, Francisco G.,Ortiz-Marciales, Margarita,Melendez, Hector J.,Correa, Wildeliz,De Jesus, Melvin