Synthesis of chiral amines using terpenyl spiroborate esters as catalysts (original) (raw)
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Organic Letters, 2007
The enantioselective borane reduction of O-benzyloxime ethers to primary amines was studied under catalytic conditions using the spiroborate esters 5 -10 derived from non-racemic 1,2-amino alcohols and ethylene glycol. Effective catalytic conditions were achieved using only 10% of catalyst 5 derived from diphenylvalinol in dioxane at 0 °C resulting in complete conversion to the corresponding primary amine in up to 99% ee.
Synthesis and stability of new spiroaminoborate esters
Tetrahedron Letters, 2012
New spiroaminoborate esters derived from 1,1-diphenylprolinol, ephedrine and dihydroquinine with different alkoxy substituents were prepared as stable crystalline compounds and characterized by spectroscopical analysis and specific rotation. The structure of the spiroborate 4 derived from 1,1-diphenylprolinol and dicyclohexyl-1,1′-diol was confirmed by X-ray analysis.
Enantioselective reduction of prochiral ketones using spiroborate esters as catalysts
Tetrahedron Letters, 2007
Novel spiroborate esters derived nonracemic 1,2-aminoalcohols and ethylene glycol are reported as highly effective catalysts for the asymmetric borane reduction of a variety of prochiral ketones with borane-dimethyl sulfide complex at room temperature. Optically active alcohols were obtained in excellent chemical yields using 0.1 to 10 mol % of catalysts with up to 99% ee.
The Journal of Organic Chemistry, 2008
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 3and 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 TIPSprotected (S)-2-amino-2-pyridylethanol in 97% ee. Supporting Information Available: Experimental procedures, physical properties and spectral data for all oximes, data characterization for known benzyl oximes and acetamides, and enantiomeric determination by chromatography for all racemic and nonracemic acetamides. This material is available free of charge via the Internet at
Helvetica Chimica Acta, 2006
The secondary reduction in the direct and oxazaborolidine-catalyzed asymmetric borane reduction of ketones was investigated by the use of GC/MS tracing titration and control experiments. The results indicate that the secondary reduction affects the enantioselectivity only in noncoordinated solvents at low temperature and not under the usual catalytic reduction conditions because the intermediate alkoxy-A C H T U N G T R E N N U N G borane is unstable and quickly converts to borane and dialkoxyborane. The function of an alcohol additive in the asymmetric borane reduction of ketones is to consume excess borane in the reduction system thus inhibiting noncatalytic reduction, which leads to increased enantioselectivity in the catalytic reduction.
Advanced Synthesis & Catalysis, 2010
The review examines the chiral amine literature from 2000-2009 (May) concerning enantioselective and diastereoselective methods for N-acylen-A C H T U N G T R E N N U N G amide and enamine reduction, reductive amination, and imine reduction. The reaction steps for each strategy, from ketone to primary chiral amine, are clearly defined, with best methods and yields for starting material preparation and final deprotection noted. Categories of chiral amines have been defined in Section 1 to allow the reader to quickly understand whether their specific target amine falls within a difficult to synthesize, or not, structural class. Amino acids are not considered in this work.