Electrochemical Reduction of a Bromo Propargyloxy Ester at Silver Cathodes in Dimethylformamide
作者:Robert J. Henderson、Nathan R. Buehler、Erick M. Pasciak、Mohammad S. Mubarak、Dennis G. Peters
DOI:10.1149/2.0031501jes
日期:——
Cyclic voltammograms for the reduction of ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-(propargyloxy)propanoate (1) at a silver cathode in dimethylformamide (DMF) containing 0.10 M tetraethylammonium tetrafluoroborate (TEABF4) exhibit several cathodic peaks, the first of which is attributed to reductive cleavage of the carbon–bromine bond. Controlled-potential (bulk) electrolyses of 1 at silver gauze
A novel palladium-catalyzed spirocyclization through sequential Narasaka–Heck cyclization, C–Hactivation and [4 + 2] annulation has been developed. In this reaction, cheap and readily available 2-chlorobenzoic acid or ethyl phenylpropiolate was employed as the C2 insertion unit to react with γ,δ-unsaturated oxime ester. The key step in this transformation is the regioselective insertion of the C2
substituted arenes using vinylsulfoxoniumylides and ynones. The addition of ynone at the γ-position of vinylsulfoxoniumylides leads to dienyl sulfoxoniumylide that can undergo selective annulation under different conditions to give m-terphenyls and parabens. Moreover, control experiments and quantum chemical calculations reveal two distinct reaction mechanisms for both annulations.
Herein, we report the synthesis of 2H-chromenes via catalyst-controlledhighlyregioselective [3 + 3] annulation of vinyl sulfoxonium ylides with quinones. Under boron-catalyzed conditions, the reaction between the ylide and quinone resulted in the formation of 2H-chromene-4-carboxylates. In contrast, a different mechanistic pathway was observed when utilizing a Ru(II) catalytic system, which led to
stereoselective cyclopropanation of vinyl sulfoxoniumylides with indane 1,3-dione and aldehydes under mild reaction conditions. In contrast to previous reports, the present work shows that electrophilic addition selectively takes place at the α-position of the vinyl sulfoxoniumylide. The interesting feature of this approach is that the multicomponent reaction selectively proceeds because of the difference