Palladium-catalyzed trisallylation of benzoxazoles and 2-aryl-1,3,4-oxadiazoles with alkyne

Abstract

In this report, a palladium catalyzed direct trisallylation of azoles with alkyne via a novel subsequent mono C(sp2)–H allylation/olefin isomerization/y-selective double C(sp3)–H allylation process was developed. A wide range of substituted trisallylated azoles bearing all quaternary carbon centers has been synthesized efficiently and with high atom economy.

Palladium/Brønsted Acid Catalysis for Hydrofunctionalizations of Alkynes: From Tsuji‐Trost Allylations to Stereoselective Methodologies

“…trisallylation of azoles (Scheme 11, a). [29] This method led to pharmaceutical relevant, C2-alkenylated azoles containing an all-carbon quaternary center. Mechanistic studies revealed that allylated benzoxazole, formed by an initial CÀ H activation step, could isomerize under a palladium-catalyzed regime.…”

“…The reactivity of palladium catalysts, in the presence of heteroarenes, was further explored developing a direct C−H trisallylation of azoles (Scheme 11, a) [29] . This method led to pharmaceutical relevant, C2‐alkenylated azoles containing an all‐ carbon quaternary center.…”

Recent Developments in Transition-Metal Catalyzed Direct C–H Alkenylation, Alkylation, and Alkynylation of Azoles

“…The hydroarylation of azoles occured at the C2 position if the C5 position was not available. In 2019, Breit and coworkers introduced an interesting cascade sequence to achieve the trisallyation of benzoxazoles catalyzed by Pd(OAc)2 using Ruphos as ligand [61]. In the proposed mechanism, the reaction starts with the generation of a Pd-hydride species through oxidative addition of the Pd-catalyst with HOPiv.…”

“…Obviously, the use of transition-metal catalyzed vinyl carboxylic acids as olefin sources with heterocycles via direct activation of C-H bonds is an attractive and atom-economic synthetic methodology. Several transition-metal coupling methodologies for the direct decarboxylative olefination have been In 2019, Breit and coworkers introduced an interesting cascade sequence to achieve the trisallyation of benzoxazoles catalyzed by Pd(OAc) 2 using Ruphos as ligand [61]. In the proposed mechanism, the reaction starts with the generation of a Pd-hydride species through oxidative addition of the Pd-catalyst with HOPiv.…”

Rhodium-Catalyzed Regio- and Diastereoselective Hydroarylation of Allenes: An Unprecedented Ene Reaction

“…In addition to C–H activation, allylic metal-complexes trapped by aromatic pronucleophiles have been evaluated as an efficient method for the hydroarylation of allenes with high regio- and enantioselectivity. In this regard, allylation of acidic aromatic scaffolds such as polyfluoroarenes and benzoxazoles via palladium and nickel catalysts was disclosed, which was subsequently exploited to electron-rich arenes through rhodium and gold catalysts (Scheme b).…”