Palladium-Catalyzed Controllable Reductive/Oxidative Heck Coupling between Cyclic Enones and Thiophenes via C–H Activation

Abstract

Herein, we report a straightforward, environmentally friendly, and controllable palladium/ligand catalytic system to enable reductive/oxidative Heck reactions of cyclic enones with thiophene or furan derivatives via C–H activation. The key to this tunable reaction is the appropriate intercepting thienyl-Pd­(II)-enolate during the enolization process. Such a controllable and economic protocol would not only provide efficient methods to construct various value-added β-heteroarylated cyclic ketones/enones but also shed light on developing other conjugate addition reactions via C–H activation.

Transition-metal-catalyzed C–H bond alkylation using olefins: recent advances and mechanistic aspects

“…In 2019, Wen and Feng reported a switchable redox Heck coupling reaction of cyclic enones 115b with thiophene or furan derivatives 115a using a palladium-ligand catalytic system (Scheme 115). 193 The corresponding product was defined by thienyl-Pd( ii )-enolate 115g during the enolization process. In the presence of a proton source, the thienyl-Pd( ii )-enolate got trapped, and effective conjugate addition of thiophene to cyclic enones took place to construct the alkylated product 115i via reductive Heck type coupling.…”

Pd-Catalyzed Intermolecular Dehydrogenative Heck Reactions of Five-Membered Heteroarenes

“…[40], (22) [45], and (23) [46]). A mixture of C-2 and C-3 cross-coupling products was obtained with allyl acetate and allyl amines, the 2 position being the most reactive (Equations (20) and (21) [37], (21) [40], (22) [45], and (23) [46]). A mixture of C-2 and C-3 cross-coupling products was obtained with allyl acetate and allyl amines, the 2 position being the most reactive (Equations (20) and (21)).…”

“…Some of the above procedures have been used for DHRs of benzothiophenes (Equations (20) [37], (21) [40], (22) [45], and (23) [46]). A mixture of C-2 and C-3 cross-coupling products was obtained with allyl acetate and allyl amines, the 2 position being the most reactive (Equations (20) and 21…”

“…Most of the above DHR methods of thiophenes were also used for the reaction of furans (Equation (1) [37], Equation 3 [22], Equations (4) and (5) [40], Equation 6 [41], Equation 7 [24], Equation 12 [44], Equation 13 [45],Equation 14[46], Equation 15 [47], Equation 16 [48], Equation 17 [49], and Equation 29 [46]). The difunctionalization of 2-butylfuran was also carried out (Equation 18 In contrast to thiophenes and benzothiophenes, thienothiophene and thienofuran react in the 3position.…”

“…), led to aldehydes or ketones (Equation (6)) through hydrogen migration [41] as that occurs from the Heck reaction of such substrates [42]. (6) Procedures using palladium associated to various ligands have been reported for olefination with acrylates, enones, acrylamides, styrenes, vinyl phosphonates, or sulfones (Equations (7) and (8) [24], Equations (9) and (10) [43], Equations (11) and (12) [44], Equation (13) [45], and Equation 14, respectively [46]). The aerobic DHR with allylic alcohols disclosed by Jiang's team (In contrast to the captions of the publication tables [41], oxygen was the sole oxidant.…”