Enhanced Excited-State Hydricity of Pd–H Allows for Unusual Head-to-Tail Hydroalkenylation of Alkenes

Abstract

Photoinduced enhancement of hydricity of palladium hydride species enables unprecedented hydride addition-like ("hydridic") hydropalladation of electron-deficient alkenes, which allows for chemoselective head-to-tail cross-hydroalkenylation of electron-deficient and electron-rich alkenes. This mild and general protocol works with a wide range of densely functionalized and complex alkenes. Notably, this approach also allows for highly challenging cross-dimerization of electronically diverse vinyl arenes and heteroarenes.

Reductive Cross-Coupling of Olefins via a Radical Pathway

“…The resulting olefin cross-coupling method complements the previously reported protocol, as the same two olefins play opposite roles (compare Figure a and b). As a result, sp 3 -dense products 3 with different connectivity, arising from opposite disconnections, become available …”

Merging of Light/Dark Palladium Catalytic Cycles Enables Multicomponent Tandem Alkyl Heck/Tsuji–Trost Homologative Amination Reaction toward Allylic Amines

“…To the best of our knowledge, cases where the same transition-metal catalyst performs two different catalytic reactions in light and dark cycles are unprecedented. Based on the above mechanistic experiments and literature reports, , the following mechanism was proposed for this three-component homologative amination reaction. It begins with the SET from photoexcited Pd(0) complex to a dielectrophile to generate a hybrid Pd­(I)/radical species A .…”

“…The success of this transformation relied on a novel activation mode of electrophiles, involving formation of hybrid Pd-radical intermediates. The follow-up reports from our group and others have significantly expanded this chemistry and types of electrophiles used . We hypothesized that this platform could be applied to some 1,1-dielectrophiles, which could engage in the alkyl Heck-type transformation for the in situ generation of an allylic intermediate i , a capable precursor for a subsequent Tsuji–Trost amination step.…”

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part B: The Hydro(hetero)arylation, Hydroalkenylation and Hydroalkylation Reactions

“…[30] Gevorgyan's team also proposed a hydridopalladium complex as the species catalyzing the lightassisted hydroalkenylation of ethyl acrylate with styrene. [31] Using palladium carboxylate associated to a phosphine in the presence of tetra-butylammonium bromide, a trialkylamine and a carboxylic acid, the authors observed a determining role of the ligand and the acid (Scheme 7a). While Pd(OCOt-Bu) 2 was only slightly better than Pd(OAc) 2 and Pd(OCOCF 3 ) 2 , Xantphos was the sole ligand leading to high yield, its exchange for DPEPhos or dtbdppf resulting in no more than 6% yield.…”

“…The best result was obtained with t-BuCO 2 H. No reaction arose in the dark and the absence of above additives was prejudicial to the yield. According to the proposed mechanism, [31] Pd 0 complex in situ formed from phosphine mediated reduction of the palladium carboxylate [32] undergoes reaction with RCO 2 H leading to palladium hydride 7bA (Scheme 7b). Light-induced addition of the latter to ethyl acrylate is followed by CÀ Pd bond homolysis providing hybrid Pd I alkyl radical species 7bB.…”