Carboxylate switch between hydro- and carbopalladation pathways in regiodivergent dimerization of alkynes
Experimental and theoretical investigation of the regiodivergent palladium-catalyzed dimerization of terminal alkynes is presented. Employment of N-heterocyclic carbene-based palladium catalyst in the presence of phosphine ligand allows for highly regio- and stereoselective head-to-head dimerization reaction. Alternatively, addition of carboxylate anion to the reaction mixture triggers selective head-to-tail coupling. Computational studies suggest that reaction proceeds via the hydropalladation pathway favoring head-to-head dimerization under neutral reaction conditions. The origin of the regioselectivity switch can be explained by the dual role of carboxylate anion. Thus, the removal of hydrogen atom by the carboxylate directs reaction from the hydropalladation to the carbopalladation pathway. Additionally, in the presence of the carboxylate anion intermediate, palladium complexes involved in the head-to-tail dimerization display higher stability compared to their analogues for the head-to-head reaction. Track changer: The regiodivergent palladium-catalyzed dimerization of terminal alkynes was studied. High regio- and stereoselectivity was achieved for both head-to-head and head-to-tail dimerization reactions. Computational studies suggest hydropalladation to favor head-to-head dimerization under neutral conditions. Addition of carboxylate anions switches the reaction from hydropalladation to carbopalladation pathway securing head-to-tail coupling (see scheme).
Zatolochnaya, Olga V.,Gordeev, Evgeniy G.,Jahier, Claire,Ananikov, Valentine P.,Gevorgyan, Vladimir
supporting information
p. 9578 - 9588
(2014/08/18)
Reactivity switch enabled by counterion: Highly chemoselective dimerization and hydration of terminal alkynes
A counterion-controlled reactivity tuning in Pd-catalyzed highly chemoselective and regioselective dimerization and hydration of terminal alkynes is reported. The use of acetate as counterion favors the formation of an alkenyl alkynyl palladium intermediate which forms hitherto less reported 1,3-diaryl-substituted conjugated enynes after reductive elimination. Using chloride, which is a better leaving group, leads to anion exchange on the alkenylpalladium intermediate with hydroxide which after reductive elimination and tautomerization delivered the hydration products.
Xu, Caixia,Du, Weiyuan,Zeng, Yi,Dai, Bin,Guo, Hao
supporting information
p. 948 - 951
(2014/03/21)
MOLECULES FOR INTRAMOLECULAR RECOGNITION. SYNTHESIS AND STRUCTURES OF DIARYL- AND ARYLNAPHTHYLETHYNES
While synthesizing models for intramolecular recognition, a simple and efficient method for forming terminal arylethynes was developed and palladium-catalyzed coupling chemistry of alkynes with either aryl iodides or aryl triflates was used to form crowde
Evans, Kevin L.,Prince, Philippe,Huang, Enoch T.,Boss, Keisha R.,Gandour, Richard D.
p. 6753 - 6756
(2007/10/02)
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