Highly stereoselective palladium-catalyzed dithiocarbonylation of propargylic mesylates with thiols and carbon monoxide

[GRAPHICS] Highly stereoselective dithiocarbonylation of propargylic mesylates with thiols and carbon monoxide has been developed by the use of tetrakis(triphenylphosphine)palladium(0) as the catalyst at 90 degreesC in THF. The reaction affords the corresponding dithioesters in good to excellent yields. For some secondary and tertiary propargylic alcohols with a terminal or internal triple bond, the reaction stereoselectively produces E-dithioesters as products. The dithiocarbonylation is believed to proceed via allenylpalladium and allenyl ester intermediates, and the high stereoselectivity might be rationalized by a mechanism where nucleophilic attack of a Pd(0)L-n species on the allenyl sp carbon occurs from the less hindered side of an alkyl substituent.