Browsing by Author "Wu, Xuesong"

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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-catalyzed diastereoselective aerobic intramolecular dehydrogenative coupling of hydrazones via sp3 C–H functionalization
    (Royal Society of Chemistry, 2015) Wu, Xuesong; Wang, Mian; Zhang, Guangwu; Zhao, Yan; Wang, Jianyi; Ge, Haibo; Department of Chemistry & Chemical Biology, School of Science
    Transition metal-catalyzed cross dehydrogenative coupling is an important tool for functionalization of the α Csp3–H bond of amines. Among this reaction category, copper-catalyzed selective C–C bond formation under atmospheric O2 is of considerable research interest and significant progress has been achieved in recent years. In comparison, development of the intramolecular version of this transformation is still in its infancy. Furthermore, diastereoselective cyclization with this transformation has not been achieved. Here, we describe the highly diastereoselective intramolecular dehydrogenative cyclization of N,N-disubstituted hydrazones by a copper-catalyzed sp3 C–H bond functionalization process. The reaction protocol utilizes O2 as the oxidant and shows great functional group compatibility. Computational studies suggest that a 5-center/6-electron disrotatory cyclization mechanism is probably involved in the process for controlling the diastereoselectivity. This work represents the first example of a copper-catalyzed, direct intramolecular diastereoselective coupling reaction via an iminium ion intermediate. Additionally, it provides an environmentally friendly and atom efficient approach to access substituted pyrazolines, an important structural unit in many biologically active compounds.
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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.
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    Direct Aerobic Carbonylation of C(sp2)-H and C(sp3)-H Bonds through Ni/Cu Synergistic Catalysis with DMF as the CO Source
    (ACS, 2015-03) Wu, Xuesong; Zhao, Yan; Ge, Haibo; Department of Chemistry & Chemical Biology, IU School of Science
    The direct carbonylation of aromatic sp2 and unactivated sp3 C–H bonds of amides was achieved via nickel/copper catalysis under atmospheric O2 with the assistance of a bidentate directing group. The sp2 C–H functionalization showed high regioselectivity and good functional group compatibility. The sp3 C–H functionalization showed high site-selectivity by favoring the C–H bonds of α-methyl groups over those of the α-methylene, β- or γ-methyl groups. Moreover, this reaction showed a predominant preference for functionalizing the α-methyl over α-phenyl group. Mechanistic studies revealed that nickel/copper synergistic catalysis is involved in this process.
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    Pyridine-enabled copper-promoted cross dehydrogenative coupling of C(sp2)–H and unactivated C(sp3)–H bonds
    (Royal Society of Chemistry, 2015-07) Wu, Xuesong; Zhao, Yan; Ge, Haibo; Department of Chemistry & Chemical Biology, School of Science
    The pyridine-enabled cross dehydrogenative coupling of sp2 C–H bonds of polyfluoroarenes and unactivated sp3 C–H bonds of amides was achieved via a copper-promoted process with good functional group compatibility. This reaction showed great site-selectivity by favoring the sp2 C–H bonds ortho to two fluoro atoms of arenes and the sp3 C–H bonds of α-methyl groups over those of the α-methylene, β- or γ-methyl groups of the aliphatic amides. Mechanistic studies revealed that sp3 C–H bond cleavage is an irreversible but not the rate-determining step, and the sp2 C–H functionalization of arenes appears precedent to the sp3 C–H functionalization of amides in this process.