Highly Selective β-Hydride Elimination in the Pd-Catalyzed Cross-Coupling of N-Tosylhydrazones with Benzyl Bromides

In Pd-catalyzed cross-coupling reactions between tosylhydra-zones and organohalides, the competitive beta-H elimination of palladium complex intermediate generated through palladium-carbene complex's migratory insertion is usually avoided by combining two specific coupling partners, in which only one contains a beta-H. To address this limitation, herein we present cross-coupling reactions between benzyl bromides and tosylhydrazones derived from benzocyclic ketones. Benzyl-substituted dihydronaphthalenes and 1H-indenes can be obtained in up to 88% yields and 25:1 selectivity for the cyclic olefin via this method. DFT studies were performed to elucidate the reaction mechanism. The beta-H elimination process, which follows the migratory insertion of Pd carbene intermediates, favours the abstraction of hydrogen atoms on the cyclic skeletons and results in the observed regioselectivity.