Browsing by Author "Li, Guigen"

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    Cobalt-catalysed site-selective intra- and intermolecular dehydrogenative amination of unactivated sp3 carbons
    (Nature Publishing Group, 2015-03-10) Wu, Xuesong; Yang, Ke; Zhao, Yan; Sun, Hao; Li, Guigen; Ge, Haibo; Department of Chemistry & Chemical Biology, School of Science
    Cobalt-catalysed sp2 C–H bond functionalization has attracted considerable attention in recent years because of the low cost of cobalt complexes and interesting modes of action in the process. In comparison, much less efforts have been devoted to the sp3 carbons. Here we report the cobalt-catalysed site-selective dehydrogenative cyclization of aliphatic amides via a C–H bond functionalization process on unactivated sp3 carbons with the assistance of a bidentate directing group. This method provides a straightforward synthesis of monocyclic and spiro β- or γ-lactams with good to excellent stereoselectivity and functional group tolerance. In addition, a new procedure has been developed to selectively remove the directing group, which enables the synthesis of free β- or γ-lactam compounds. Furthermore, the first cobalt-catalysed intermolecular dehydrogenative amination of unactivated sp3 carbons is also realized., Functionalizing unactivated carbon–hydrogen bonds is challenging, especially when using non-precious metals and dealing with sp3 hybridized carbons. Here, the authors report an intramolecular cobalt catalysed amination of C–H bonds of sp3 carbons, giving access to β- and γ-lactams.
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    Copper-promoted site-selective carbonylation of sp3 and sp2 C–H bonds with nitromethane
    (RSC, 2016-08) Wu, Xuesong; Miao, Jinmin; Li, Yanrong; Li, Guigen; Ge, Haibo; Department of Chemistry & Chemical Biology, School of Science
    Copper-promoted direct carbonylation of unactivated sp3 C–H and aromatic sp2 C–H bonds of amides was developed using nitromethane as a novel carbonyl source. The sp3 C–H functionalization showed high site-selectivity by favoring the C–H bonds of α-methyl groups. The sp2 C–H carbonylation featured high regioselectivity and good functional group compatibility. Kinetic isotope effect studies indicated that the sp3 C–H bond breaking step is reversible, whereas the sp2 C–H bond cleavage is an irreversible but not the rate-determining step. Control experiments showed that a nitromethyl intermediate should be involved in the present reaction.