for α,β-disubstituted α,β-unsaturated esters is performed via three general and robust reaction sequences: (i) Ti−Claisen condensation (formylation) of esters to give α-formyl esters (12 examples, 60−99%), (ii) (E)- and (Z)-stereocomplementary enol p-toluenesulfonylation (tosylation) using TsCl−N-methylimidazole (NMI)−Et3N and LiOH (24 examples, 82−99%), and (iii) stereoretentive Suzuki−Miyaura cross-coupling
Triethylamine-induced Reactions of Methyl 2,3-Dibromo-2,3-diarylpropanoates in Methanol†
作者:Mercedes A. Badajoz、Rosana S. Montani、Mercedes C. Cabaleiro
DOI:10.1039/a706372e
日期:——
The title compounds undergo elimination with methanolic triethylamine to afford the corresponding debrominated olefins, most of them through an E2 stereoconvergent process.
P(NMe<sub>2</sub>)<sub>3</sub>-Mediated Umpolung Alkylation and Nonylidic Olefination of α-Keto Esters
作者:Sunewang Rixin Wang、Alexander T. Radosevich
DOI:10.1021/acs.orglett.5b01784
日期:2015.8.7
A commercial phosphorus-based reagent (P(NMe2)(3)) mediates,umpolung alkylation of methyl aroylformates with benzylic and allylic bromides, leading to either Barer-type addition or ylide-free olefination products upon workup. The reaction sequence is initiated, by a two-electron redox addition of the tricoordinate phosphorus reagent with an alpha-keto ester Compound (Kukhtin-Ramirez addition). A mechanistic rationale is offered for the chemoselectivity upon which the success of this nonmetal mediated C-C bond forming strategy is based.
Reactions of chlorine substituted (E)-2,3-diphenylpropenoic acids over cinchonidine-modified Pd: Enantioselective hydrogenation versus hydrodechlorination
The effect of the chlorine position on the C-Cl bond hydrogenolysis and the enantioselective hydrogenation of Cl substituted (E)-2,3-diphenylpropenoic acid derivatives has been studied over cinchonidine-modified Pd/Al2O3. In contrast to the fast hydrodechlorination of the beta-phenyl-para-Cl substituted acids the Cl on the alpha-phenyl ring was barely hydrogenolized. These observations were interpreted by the different arrangements of the two phenyl rings on the surface, with the alpha- and beta-phenyl rings adsorbed tilted and parallel, respectively. The results confirmed the beneficial effect of the alpha-phenyl-ortho-substituents on the chiral discrimination, thus the 2,3-diphenylpropionic acids substituted by Cl on the alpha-phenyl ring could be prepared in good yields and optical purities. The conclusions were used for the rational design of an acid, i.e. (E)-2-(2-methoxyphenyl)-3-(3,4-difluorophenyl)propenoic acid, which afforded the best optical purity (ee up to 95% at 295 K) described until now in this heterogeneous system. (C) 2010 Elsevier B.V. All rights reserved.
Badajoz, Mercedes A.; Montant, Rosana S.; Cabaleiro, Mercedes C., Journal of the Chemical Society. Perkin Transactions 2 (2001), 1996, vol. 8, p. 1717 - 1722
作者:Badajoz, Mercedes A.、Montant, Rosana S.、Cabaleiro, Mercedes C.