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Palladium(II)-Catalyzed Directed anti-Hydrochlorination of Unactivated Alkynes with HCl

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journal contribution
posted on 07.03.2017, 00:00 by Joseph Derosa, Annabelle L. Cantu, Mark N. Boulous, Miriam L. O’Duill, Joshua L. Turnbull, Zhen Liu, Daizy M. De La Torre, Keary M. Engle
A regio­selective anti-hydrochlorination of unactivated alkynes is reported. The reaction utilizes in situ generated HCl as the source of both the Cl and H+ and is catalyzed by palladium­(II) acetate, with loadings as low as 25 ppm. Removable picolinamide and 8-aminoquinoline bidentate directing groups are used to control the regio­selectivity of the chloropalladation step and stabilize the resulting alkenylpalladium­(II) intermediate for subsequent protodepalladation. This method provides access to a broad array of substituted alkenyl chlorides in excellent yields and with high regio­selectivity. The products from this transformation were successfully derivatized via Stille coupling to a variety of trisubstituted alkene products. Reaction progress kinetic analysis was performed, shedding light on a possible mechanism for this catalytic process.