![]() Et 4NI is employed as the supporting electrolyte. Prompted by the precedents on Co-catalyzed electroreduction of aryl halides 57, 58, 59, we initiated the present study with the exploration of enyne 1a as starting material in the presence of CoI 2 and phosphine ligand with Zn as sacrificial anode and Ni foam as cathode in CH 3CN at 80 oC (Table 1). Herein, we report our progress on the cobalt-catalyzed asymmetric intramolecular reductive coupling of enynes, affording chiral five-membered cyclic compounds, which represents the rare progress on the cobalt-catalyzed enantioselective transformation via electrochemistry with a general substrate scope (Fig. To our best knowledge, there is only one enantioselective report involving cobalt via electrochemistry, in which moderate enantioselectivity was reported with one single example (Fig. However, rare examples have been realized in the field of asymmetric electrosynthesis 51, 52, 53, 54, 55. These advantages render electrochemistry a sustainable, economical technique for chemical synthesis. ![]() Such tuning is impossible in the use of organic reductants or photocatalysis. Because the reduction potential and current can be adjusted, electrochemistry offers precise, selective formation of reactive species, thus avoids designing a new reagent. Recently, electrosynthesis has been revived as a reliable alternative to the conventional methods and could be utilized to replace hazardous reductants by electric current 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50. 1a, where the catalytic amount of reductant is used to initiate the catalytic cycle, reductive couplings are generally achieved via the use of stoichiometric amount of metallic reductants 24, 25, 26, organo- metallic reagents 27 or photocatalysis 28. Despite these advances, cobalt-catalyzed asymmetric intramolecular reductive coupling of 1,6-enyne has rarely been realized, which, if successful, would provide a protocol for stereoselective construction of ring systems decorated with exocyclic trisubstituted C = C bonds 23.ĭifferent from the known transformations shown in Fig. ![]() Most of these reactions are proposed to be initiated by the formation of low-valent cobalt species, which promotes the alkyne/alkene oxidative cyclization to form a cobaltacyclopentane intermediate, followed by the subsequent transformation. ![]() Known methods include cyclization 17, 18, hydrosilylation 19, homo-ene cyclization 20, hydroarylative 21 and hydroacylative cyclization 22, depending on the functional groups and the experimental conditions. Recently, cobalt has emerged as a cost-effective alternative in the enantioselective cyclization-coupling reaction of 1,6-enynes and reveals unique reactivity patterns (Fig. In these methods, noble metals have been most widely explored as the foremost studied catalyst 10, 11, 12, 13, 14, 15, 16. To this end, 1,6-enynes have emerged as versatile substrates in catalytic reactions to prepare cyclic skeletons with a broad range of functional moieties, which enable the direct transformation of a linear substrate to a cyclic product 1, 2, 3, 4, 5, 6, 7, 8, 9. The stereoselective synthesis of optically active functionalized carbo- and heterocycles receives significant attention in organic synthesis due to the prevalence of these chiral scaffolds in the core structures of numerous bioactive natural products and pharmaceuticals. ![]()
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