Baiquan Wang

Bio: Baiquan Wang is an academic researcher from Nankai University. The author has contributed to research in topics: Annulation & Ruthenium. The author has an hindex of 31, co-authored 84 publications receiving 3297 citations. Previous affiliations of Baiquan Wang include Chinese Academy of Sciences & Peking University.

Ruthenium-catalyzed isoquinolone synthesis through C-H activation using an oxidizing directing group.

Abstract: The redox neutral strategy circumvents the use of wasteful metal oxidants and leads to a clean process.

Rhodium-catalyzed cascade oxidative annulation leading to substituted naphtho[1,8-bc]pyrans by sequential cleavage of C(sp2)-H/C(sp3)-H and C(sp2)-H/O-H bonds.

Abstract: The cascade oxidative annulation reactions of benzoylacetonitrile with internal alkynes proceed efficiently in the presence of a rhodium catalyst and a copper oxidant to give substituted naphtho[1,8-bc]pyrans by sequential cleavage of C(sp2)–H/C(sp3)–H and C(sp2)–H/O–H bonds. These cascade reactions are highly regioselective with unsymmetrical alkynes. Experiments reveal that the first-step reaction proceeds by sequential cleavage of C(sp2)–H/C(sp3)–H bonds and annulation with alkynes, leading to 1-naphthols as the intermediate products. Subsequently, 1-naphthols react with alkynes by cleavage of C(sp2)–H/O–H bonds, affording the 1:2 coupling products. Moreover, some of the naphtho[1,8-bc]pyran products exhibit intense fluorescence in the solid state.

Direct Cross‐Coupling of CH Bonds with Grignard Reagents through Cobalt Catalysis

Abstract: Many methods have recently been developed to construct C C bonds through direct C H transformations. Among these methods, various transition metals have been shown to be effective in the last two decades. 3] The first-row transitionmetal catalysts, such as iron complexes, 5] have drawn much attention recently as a result of their ready availability, low cost, relatively low toxicity, and unique catalytic abilities. Cases where the catalytic direct C H transformation is mediated by Co catalysis are very rare. On the other hand, various organometallic reagents have been successfully used to facilitate such transformations. However, much more active Grignard reagents have never been successfully applied as an intermolecular coupling partner with C H bonds. Herein, we demonstrated the first successful example of cobalt-catalyzed direct C H transformation with both aryl and alkyl Grignard reagents as nucleophiles to facilitate C C bond formation. In other studies, the directing group orientation was considered useful to control the regioselectivity in C H activation. Among different anchoring groups, nitrogencontained groups were frequently used owing to their good compatibility with transition metals and synthetic applications. 7h, 9] Initially, we chose the benzo[h]quinoline (1a) as the substrate to explore the reactivity of Grignard reagents in the presence of transition-metal catalysts. However, in the absence of any catalyst, the direct nucleophilic attack of pyridine derivatives at the 2-position by Grignard reagents is a big challenge (traditional pathway, Scheme 1). For instance, even much less active organozinc reagents promote such a reaction through nickel catalysis. We propose that the presence of a suitable transition-metal catalyst and lowering the reaction temperature might be the good strategy to decrease the reactivity of RMgBr toward the direct addition to pyridine derivatives. After many trials to achieve the goal, the desired crosscoupling finally took place smoothly with Co(acac)3 as a catalyst in the presence of TMEDA and DCB in THF at room temperature (Table 1, entry 1). Certainly, no desired product 3aa was formed in the absence of catalyst, under otherwise identical conditions with Grignard reagents. Next, the reactivity of various Grignard reagents was investigated (Table 1). Phenyl Grignard reagents bearing different substituents provided the desired products in moderate to excellent yields. The steric effect was important in influencing the reaction outcome. Thus, increase of the steric hindrance dramatically decreased the yield (compare Table 1, entries 2, 3, and 4). Meanwhile, further increase of steric hindrance completely inhibited the transformation (Table 1, entry 14). Importantly, the functional groups MeO (Table 1, entries 8 and 9), F (Table 1, entry 11), and Cl (Table 1, entry 12) are compatible. These findings offer the opportunity for the orthogonal coupling to afford more complicated molecules. This direct cross-coupling can be extended to alkyl Grignard reagents for the constructions of C(sp) C(sp) bonds. Interestingly, MeMgBr showed the best reactivity and the desired methylated product 3aq was isolated in an excellent yield (Table 1, entry 17). However, other alkyl Grignard reagents gave much lower yields and only linear products were obtained (Table 1, entries 18–21). Unfortunately, under the same conditions, vinylMgBr completely failed to facilitate this cross-coupling reaction (Table 1, entry 22). Moreover, different benzo[h]quinoline compounds were investigated (Scheme 2). We found that this transformation was very sensitive to steric effects. When either a Ph or Me group was introduced at the 2-position, the coupling was completely inhibited and only the starting material was recovered (3ba and 3ca). If the substituent was introduced at the 9-position, the cross-coupling indeed took place while Scheme 1. New catalytic pathway beyond the traditional nucleophilic addition of RMgBr in the presence of a Co catalyst.

Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications

Abstract: Catalytic transformation of ubiquitous C–H bonds into valuable C–N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C–H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

3d Transition Metals for C-H Activation.

Abstract: C–H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C–H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C–H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C–H activation until summer 2018.

Carboxylate-assisted ruthenium-catalyzed alkyne annulations by C-H/Het-H bond functionalizations.

Abstract: To improve the atom- and step-economy of organic syntheses, researchers would like to capitalize upon the chemistry of otherwise inert carbon–hydrogen (C–H) bonds. During the past decade, remarkable progress in organometallic chemistry has set the stage for the development of increasingly viable metal catalysts for C–H bond activation reactions. Among these methods, oxidative C–H bond functionalizations are particularly attractive because they avoid the use of prefunctionalized starting materials. For example, oxidative annulations that involve sequential C–H and heteroatom–H bond cleavages allow for the modular assembly of regioselectively decorated heterocycles. These structures serve as key scaffolds for natural products, functional materials, crop protecting agents, and drugs. While other researchers have devised rhodium or palladium complexes for oxidative alkyne annulations, my laboratory has focused on the application of significantly less expensive, yet highly selective ruthenium complexes.This Ac...