科研之友
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摘要
Density functional theory calculations were employed to elucidate the mechanism of Mn-catalyzed chemoselective hydroarylation reactions. The Mn-catalyzed [4+2] annulation undergoes a reaction pathway involving sequential imine-directed C-H bond cleavage, alkyne insertion into the Mn-C bond, beta-oxygen elimination and outer catalytic cycle annulation-aromatization. Computational results demonstrated that the previously proposed chelation-assisted alkyne insertion process was unfavorable owing to the weak coordination ability of the beta-oxygen leaving group compared with that of CO. Further noncovalent interactions analysis indicated that the origin of the high regioselectivity was contributed to the steric repulsion resulting from significant nonbonding overlap between the reacting aryl moiety and the quaternary carbon group of the reactant in the alkyne insertion step. In addition, in the Bronsted-acid-mediated chemoselective alkenylation reaction, the used terminal alkynes had relatively enhanced reactivity in the alkyne insertion step owing to its reduced steric repulsion. From the active alkenyl-Mn intermediate, the activation free energy of protonation and beta-oxygen elimination are approximate, thus the alkenylated product is obtained after protonation in an acidic system. We expect that this detailed mechanistic study will significantly enhance our ability to develop Mn-catalyzed arene C-H bond functionalization reactions.
