Ynolates were found to react with alpha-alkoxy-, alpha-siloxy-, and alpha-aryloxyketones at room temperature to afford tetrasubstituted olefins with high Z selectivity. Since the geometrical selectivity was determined in the ring opening of the beta-lactone enolate intermediates, the torquoselectivity was controlled by the ethereal oxygen atoms. From experimental and theoretical studies, the high Z
Additions of Organomagnesium Halides to α-Alkoxy Ketones: Revision of the Chelation-Control Model
作者:Jacquelyne A. Read、Yingying Yang、K. A. Woerpel
DOI:10.1021/acs.orglett.7b01161
日期:2017.7.7
obtained in additions of organometallic nucleophiles to α-alkoxy ketones but fails for reactions of allylmagnesium halides. Low diastereoselectivity in ethereal solvents results from no chelation-induced rate acceleration. Additions of allylmagnesium bromide to carbonyl compounds are diastereoselective using CH2Cl2 as the solvent even though rate acceleration is still absent. Stereoselectivity likely arises
Chelates as intermediates in nucleophilic additions to alkoxy ketones according to Cram's rule (cyclic model)
作者:Xiangning Chen、Edwin R. Hortelano、Ernest L. Eliel、Stephen V. Frye
DOI:10.1021/ja00031a036
日期:1992.2
Chelates have been considered intermediates in the often highly stereoselective reactions of α-alkoxy and similarly substituted ketones for over 30 years, 10 but without mechanistic evidence
Conformationally Biased Ketones React Diastereoselectively with Allylmagnesium Halides
作者:Nicole D. Bartolo、Krystyna M. Demkiw、Jacquelyne A. Read、Elizabeth M. Valentín、Yingying Yang、Alexandra M. Dillon、Chunhua T. Hu、Michael D. Ward、K. A. Woerpel
DOI:10.1021/acs.joc.1c02844
日期:2022.3.4
The addition of the highly reactive reagent allylmagnesium halide to α-substituted acyclic chiral ketones proceeded with high stereoselectivity. The stereoselectivity cannot be analyzed by conventional stereochemical models because these reactions do not conform to the requirements of those models. Instead, the stereoselectivity arises from the approach of the nucleophile to the most accessible diastereofaces
高反应性试剂烯丙基卤化镁与α-取代的无环手性酮的加成具有高立体选择性。立体选择性无法通过常规立体化学模型进行分析,因为这些反应不符合这些模型的要求。相反,立体选择性是由于亲核试剂接近酮的最低能量构象的最容易接近的非对映面而产生的。预期具有高立体选择性,并且可以预测立体化学结果,其中构象偏向的酮具有空间上可区分的非对映面,其中只有一个面可进行亲核加成。酮的构象可以通过计算建模和在某些情况下通过 X 射线晶体学确定结构的组合来确定。
Are chelates truly intermediates in Cram's chelate rule?
作者:Xiangning Chen、Edwin R. Hortelano、Ernest L. Eliel、Stephen V. Frye