Diastereoselectivity of Enolate Anion Protonation. H/D Exchange of -Substituted Ethyl Butanoates in Ethanol-d

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• 作者：Jerry R. Mohrig ; Robert E. Rosenberg ; John W. Apostol ; Mark Bastienaansen ; Jordan W. Evans ; Sonya J. Franklin ; C. Daniel Frisbie ; Sabrina S. Fu ; Michelle L. Hamm ; Christopher B. Hirose ; David A. Hunst
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：January 22, 1997
• 年：1997
• 卷：119
• 期：3
• 页码：479 - 486
• 全文大小：196K
• 年卷期：v.119,no.3(January 22, 1997)
• ISSN：1520-5126

文摘

The stereochemistry of base-catalyzed H/D exchange on 13-substituted ethyl butanoates in ethanol-dhas been studied in order to analyze the steric and electronic factorswhich control the diastereoselectivity ofelectrophilic attack on enolate anions. Electrophilic deuterationof the enolate anion also determines the stereoselectivityof 1,4-conjugate addition of ethanol-d to,-unsaturated esters. Experimental conditions were selectedwhichrigorously exclude the effects of ion pairing and aggregation. Theresearch showed that stereoelectronic factorsgenerally produce higher stereoselection than steric effects do.Electronegative heteroatom substituents at C-3produceda 10:1 ratio of the2R*,3R*/2R*,3S*2-deuteriobutanoates. In the most stable transition states forelectrophilic attack,these electronegative substituents occupy an antiperiplanar position tothe forming C-D bond. Only with a-tert-butyl substituent did steric effects produce high stereoselection, andit fell off rapidly with a decrease in carbonbranching. Protonation of acyclic -ethoxy aldehyde and ketoneenolates follows the same diastereoselectivity patternas the -ethoxy ester enolate, but protonation of the cyanocarbanionfrom a -ethoxy nitrile gives much lowerstereoselection.