Angelw: cobalt catalyzed cross coupling reaction of alkenyl acetate with aryl or alkenyl zinc reagents

Aryl or heteroaryl zinc reagents have a wide range of functional group tolerance Among them, aryl zinc pentanoate reagent has good stability and can be stored in argon for several months Under the catalysis of transition metal, unsaturated tevalate or acetate can be used as electrophilic reagent to couple with organometallic reagents derived from boron, silicon, zinc, aluminum and magnesium However, toxic transition metal catalysts such as rhodium or nickel are often needed for such conversion Due to the low toxicity and abundant reserves of cobalt, the cross coupling catalyzed by cobalt has unique advantages in industry and green synthesis Gosmini and his collaborators have developed cobalt catalyzed cross coupling of aryl halides with vinyl acetate, but the range of substrates is limited (Tetrahedron 2003, 59, 2999-3002) Ackermann's team reported the direct c-h-linked olefinization of indole and alkenylacetate catalyzed by cobalt Nitrogen Heterocyclic Carbene (angew Chem Int ed 2015, 54, 6352-6355) Recently, the research group of Professor Paul knockel of the University of Munich in Germany reported a kind of cross coupling reaction of alkenyl acetate with aryl or alkenyl zinc reagents catalyzed by cobalt in the international authoritative magazine, angelw Chem Int ed., which has mild reaction conditions and a wide range of functional group tolerance and stereoselectivity The first author of the paper is Li Jie, researcher of Jiangnan University, and the corresponding author is Professor Paul knockel (DOI: 10.1002 / anie 201805486) Firstly, the reaction conditions were screened with phznopiv 1a and alkenyl acetate 2A as substrates The reaction can not take place without metal or with Cui, Fe (ACAC) 2 as catalyst At room temperature, with 5 mol% cobr 2 as catalyst and 2,2 '- bipyridine (bpy) as ligand, the target product 3A (Table 1) can be obtained in 87% yield (source: angelw Chem Int ed.) later, the author investigated the substrate range of the reaction (table 2-2) The aryl zinc reagent can be prepared by the method shown in table 2-1 Under the optimized reaction conditions, a variety of aryl zinc reagents can be coupled with 2a to obtain the corresponding target products The ring size of cyclic alkenylacetate has no obvious effect on the reaction In addition, 4-acetyl-6-methyl-2-pyranone and 4-acetylcoumarinone can also react with 1a, and the product yield is good (source: angelw Chem Int ed.) the author found that under this reaction condition, alkenylsulfonate 4 can also be coupled with arylzinc reagent (Table 3) This kind of reaction has high selectivity E-alkenes can be obtained from the reaction of e-alkenesulfonate or z-alkenesulfonate with 1a However, the mixture of Z / E = 1:1 can only be obtained when the electron deficient aryl zinc reagent reacts with 4A for 1H (source: angelw Chem Int ed.) next, the author investigated the reactivity of styryl acetate (Table 4) The reaction can take place when the benzene ring contains electron absorption group or electron donor group The reaction of 6G (E / Z 2:1) of styryl acetate with 1I can produce 7g of the product in the ratio of E / z = 99:1; the reaction of 6h of 2-propenyl acetate with 1g can also produce the target with excellent yield (source: angelw Chem Int ed.) 1,3-diene is widely found in natural products and bioactive compounds It is found that the coupling reaction of 1,3-diene acetate with alkyl or aryl zinc reagents can also proceed smoothly under this condition (scheme 1) (source: angelw Chem Int ed.) finally, in order to prove the practical application value of the reaction, the author synthesized the estrogen derivatives 12a and 12b (scheme 2) by α - oxcarbonylation, esterification and cross coupling reaction catalyzed by cobalt with estrone compound 10 as the starting material (source: angelw Chem Int ed.) conclusion: Professor Paul knockel, University of Munich, Germany, reported a kind of cross coupling reaction of alkenyl acetate with aryl or alkenyl zinc reagents catalyzed by cobalt The reaction conditions are mild, which is completed at room temperature, and has a wide range of substrate applicability and stereoselectivity Two estrogen derivatives were synthesized by this reaction, which further proved the potential application value of this reaction.