Asymmetric Reduction of Imines with Trichlorosilane, Catalyzed by Sigamide, an Amino Acid-Derived Formamide: Scope and Limitations

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• 作者：Andrei V. Malkov ; Kvetoslava Vrankov ; Sigitas Stonius ; Pavel Koovsk
• 刊名：Journal of Organic Chemistry
• 出版年：2009
• 出版时间：August 21, 2009
• 年：2009
• 卷：74
• 期：16
• 页码：5839-5849
• 全文大小：920K
• 年卷期：v.74,no.16(August 21, 2009)
• ISSN：1520-6904

文摘

Enantioselective reduction of ketimines 6−10 with trichlorosilane can be catalyzed by the N-methyl valine-derived Lewis-basic formamide (S)-23 (Sigamide) with high enantioselectivity (≤97% ee) and low catalyst loading (1−5 mol %) at room temperature in toluene. The reaction is efficient with ketimines derived from aromatic amines (aniline and anisidine) and aromatic, heteroaromatic, conjugated, and even nonaromatic ketones 1−5, in which the steric difference between the alkyl groups R¹ and R² is sufficient. Simple nitrogen heteroaromatics (8a,b,d) exhibit low enantioselectivities due to the competing coordination of the reagent but increased steric hindrance in the vicinity of the nitrogen (8c,e) results in a considerable improvement. Cyclic imines 32d-d exhibited low to modest enantioselectivities.