Unique regio- and stereoselectivity in Pd-catalyzed chlorocarbonylation reaction of 2-phenylethynyl selenides and 2-alkylethynyl selenides. Highly stereoselective synthesis of 2-seleno-3-chloroacrylates

Regio- and stereoselectivity in the chloropalladation carbonylation reaction of different acetylenic selenides in the presence of 0.05 equiv of PdCl2 and 3 equiv of cupric chloride under 1 atm of carbon monoxide affording 2-seleno-3-chloroacrylates were investigated. Opposite stereoselectivities were observed with 2-phenylethynyl selenides and 8-alkylethynyl selenides the reactions of 2-phenylethynyl selenides afforded (E)-2-seleno-3-chloro-3-phenylacrylates, while the reactions of 8-alkyl-ethynyl selenides gave (Z)-2-seleno-3-chloro-3-alkylacrylates. A chloropalladation carbonylation mechanism for this reaction was proposed. The regio- and stereoselective chloropalladation of the carbon-carbon triple bond in acetylenic selenides affords 1-enylpalladium intermediates, in which : the palladium atom connects with the carbon atom bonding with the selenium atom. Carbonylation in the presence of an alcohol affords 2-seleno-3-chloroacrylates.