β-Hydrogen Elimination to Access a PdH Catalyst for Hydroalkenylation and Hydroalkylation

Transition metal alkyl species are widespread intermediates and prefer to undergo the β-H elimination process to release HX, which results in β-H loss. Alkyl electrophiles are usually used as radical donors in alkyl Heck reaction, and the undesired β-H elimination needs to be suppressed. Herein, we report a β-hydrogen elimination-enabled PdH-catalyzed hydrofunctionalization of alkyl halides with gem-fluoroalkenes or N-tosylhydrazones under visible-light irradiation. β-H elimination of the alkyl-palladium intermediates (generated from alkyl halide partners) access catalytic Pd–H species and alkenes. This is followed by regioselective migratory insertion of gem-fluoroalkene or carbene into the Pd–H bond and subsequent alkyl Heck reaction with the in situ generated alkene (from alkyl halide) to afford the final hydroalkenylation or hydroalkylation product. These products can undergo a variety of valuable transformations. Notably, two drug compounds, flobufen and imazodan, can be synthesized to demonstrate the utility of this protocol. Experimental and computational studies provide insight into the reaction mechanism. Compared to systems using alkyl halides as radical precursors, this system switches alkyl halides from radical donors to acceptors (alkenes) and provides a strategy for the intermolecular hydrogen-transfer alkyl Heck reaction of alkyl halides.