Angelw: cobalt catalyzed series cyclization of subalkylcyclopropane and arylamide

Transition metal catalyzed C-C bond breaking reaction is an efficient method to construct molecular framework Alkanes with tension have been widely used in C-C bond breaking reactions catalyzed by various transition metals Among them, subalkylcyclopropane has a high ring tension energy (≈ 38.8 kcal mol-1), which shows a unique activity in C-C bond breaking reactions In 2013, Cui SunLiang's group reported the intramolecular C-H activation / cycloaddition reaction of furan derivatives and subalkylcyclopropane catalyzed by rhodium When benzamide was used as the substrate, the phenomenon of C-C bond breaking (scheme 1a) was not observed Recently, Ackermann's group reported the C-H / C-C bond activation of electron absorbing methylene cyclopropane catalyzed by manganese (I) However, there is no "one pot method" for the continuous activation of C-H / C-C / C-H bonds by transition metal catalysis Recently, the research group of Fuk Yee Kwong, Chinese University of Hong Kong, reported the first method of cobalt catalyzed one-step construction of two C-C bonds of benzamide and subalkylcyclopropane to form 1,2-dihydronaphthalene derivatives The reaction includes a series of C-H activation / β - C elimination / C-H activation process Relevant articles were published in angelw Chem Int ed (DOI: 10.1002/anie.201801706) (source: angelw Chem Int ED) at the beginning of the study, the author explored the feasibility of the series reaction catalyzed by cheap cobalt complex In the toluene solution of Catalyst Co (OAC) 2 and oxidant agoac, the expected cyclization product 3A can be obtained with 46% yield by the reaction of 2-methyl-n - (8-quinolinyl) benzamide (1a) and 1-cyclopropylmethyl-4-methoxybenzene (2a) After a lot of optimization, the author found that when CO (OAC) 2 (20 mol%), PPH 3 (20 mol%) and agoac (3.0 equiv) were used in toluene, the yield of 3A was 76% After obtaining the optimal reaction conditions, the author then investigated the substrate application range of the reaction (Table 1) The results show that a series of substituted benzenesulfonamide can get the corresponding products in medium yield (49% - 79%) It is worth noting that furan and thiophenamide are also cyclized in good yield (source: angelw Chem Int ED) next, the author investigated the universality of subalkylcyclopropane (Table 2) Most of the reactions were carried out smoothly, and the corresponding 1,2-dihydronaphthalene derivatives were obtained in medium to good yields (source: angelw Chem Int ED) after a lot of mechanism experiments, the author proposed a reasonable scheme 6 At first, benzoamide (1) was coordinated with trivalent cobalt produced by CO (OAC) 2 oxidation, and then ligand exchange formed complex I; I produced intermediate II through irreversible C-H cobalt metallization; then cobalt (III) center of intermediate II was coordinated with subalkylcyclopropane, and then transferred and inserted to obtain seven membered cyclometal complex IV; it eliminated by β - C to form eight membered intermediate v Interestingly, V did not get lactam derivatives through C-N bond reduction, but experienced two possible pathways to produce cobalt complex VIII In route a, VIII is formed by intramolecular metallization of C-H cobalt; in route B, the intermediate V is obtained by intramolecular single electron transfer (set) to obtain free radical cation intermediate VI, then oxidized to obtain cobalt (III) complex VII, and then through a single electron transfer to obtain intermediate VIII In the presence of tempo, the coupling product of VI or VII with tempo was not observed, so path a is more advantageous than path B Finally, the target product was obtained by reduction, elimination and protonation of VIII In this process, the cobalt species (I) was re oxidized to cobalt (III) to complete the catalytic cycle (source: angelw Chem Int ED) Summary: Fuk Yee Kwong group has realized the process of series C-H activation / C-C cracking / C-H cyclization of aromatic amide and subalkylcyclopropane catalyzed by cobalt for the first time, which has the characteristics of good functional compatibility and wide range of substrates.