Palladium-Catalyzed Aerobic Dehydrogenation of Carbon-Carbon Bonds

描述(由申请人提供)：本提案中概述的研究针对一类新的“C-H官能化”反应，涉及Pd催化的脂肪族碳-碳单键脱氢生成芳香族、杂芳族和烯烃产品。这些反应在合成药物和生物活性分子方面应该有广泛的用途。这一新的反应活性将建立在有氧氧化催化的最新进展的基础上，使分子氧能够作为化学计量氧化剂/氢受体，形成水作为反应的唯一副产品。旨在开发新的Pd催化剂和研究其合成应用的经验研究将得到系统的机理研究的补充，以建立有助于成功反应的基本原理。主要针对四种不同类型的反应：(1)环己酮和环己酮的脱氢反应以制备各种取代苯酚衍生物，(2)酮和其他羰基化合物的脱氢反应以制备多种1，2-不饱和羰基化合物，(3)环己烯的脱氢反应以制备各种取代芳烃，以及(4)六元氮杂环的脱氢反应以制备喹啉和吡啶的衍生物。这些反应的底物可以通过多种合成路线从现成的原料中获得，包括Diels-Alder环加成反应、Robinson环合反应以及简单的缩合和加成反应。这些脱氢反应中的关键步骤包括PdII介导的C-H键的活化，通常是从相对活跃的位置(例如，靠近羰基或在烯丙基位置)，形成PdII-烷基中间体，然后2-氢化物消除以产生不饱和产物和PdII-氢化物中间体。用分子氧氧化PdII-H物种可再生活性PdII催化剂。Pd催化剂的新配体的确定将在这项工作中发挥重要作用，因为这些配体在涉及有机底物的反应中调节PdII的反应活性，并在催化剂再氧化过程中稳定Pd的还原形式(Pd0和PdII-H)。总体而言，用于C-C键有氧脱氢的高效新催化剂的开发，加上这些反应易于合成各种有机底物，将为选择性取代芳香族和杂芳族化合物提供环境友好的途径，这些化合物可以与有机化学中一些最强大的合成转化相媲美或超过，例如金属催化的交叉偶联反应。 与公共卫生相关：开发有效的有机分子合成方法对于药物和治疗剂的发现、开发和商业化生产至关重要。这项提案中概述的研究将导致制备此类生物活性分子的新催化方法。

DESCRIPTION (provided by applicant): The research outlined in this proposal targets a new class of "C-H functionalization" reactions, involving Pd-catalyzed dehydrogenation of aliphatic carbon-carbon single bonds to form aromatic, heteroaromatic and alkene products. These reactions should have widespread utility in the synthesis of pharmaceuticals and biologically active molecules. This novel reactivity will build upon recent advances in aerobic oxidation catalysis to enable molecular oxygen to serve as the stoichiometric oxidant/hydrogen acceptor, forming of water as the sole byproduct of the reaction. Empirical studies directed toward the development of new Pd catalysts and investigation of their synthetic applications will be complemented by systematic mechanistic studies to establish the fundamental principles that contribute to successful reactivity. Four different classes of reactions are targeted: (1) dehydrogenation of cyclohexanones and cyclohexenones to prepare a variety of substituted phenol derivatives, (2) dehydrogenation of ketones and other carbonyl compounds to prepare versatile 1,2-unsaturated carbonyl compounds, (3) dehydrogenation of cyclohexenes to prepare a variety of substituted arenes, and (4) dehydrogenation of 6-membered nitrogen heterocycles to prepare quinoline and pyridine derivatives. Substrates for these reactions can be obtained from readily available starting materials via a number of versatile synthetic routes, including Diels-Alder cycloadditions, Robinson annulations, and simple condensation and addition reactions. Key steps in these dehydrogenation reactions include PdII-mediated activation of a C-H bond, often from a relatively activated site (e.g., adjacent to a carbonyl group or in an allylic position), to form a PdII- alkyl intermediate, followed by 2-hydride elimination to produce the unsaturated product and a PdII-hydride intermediate. Oxidation of the PdII-H species by molecular oxygen regenerates the active PdII catalyst. The identification of new ligands for the Pd catalysts will play an important role in this work because the ligands are critical to modulate the reactivity of PdII in the reactions involving the organic substrate and to stabilize the reduced forms of Pd (Pd0 and PdII-H) in the catalyst reoxidation process. Overall, the development of efficient new catalysts for aerobic dehydrogenation of C-C bonds, together with the ease of synthetic access to diverse organic substrates for these reactions, will provide environmentally benign routes to selectively substituted aromatic and heteroaromatic compounds that rival or surpass the utility of some of the most powerful synthetic transformations in organic chemistry, such as metal-catalyzed cross-coupling reactions. PUBLIC HEALTH RELEVANCE: The development of efficient methods for the synthesis of organic molecules is critical for the discovery, development and commercial production of pharmaceuticals and therapeutic agents. The research outlined in this proposal will lead to new catalytic methods for the preparation of such biologically active molecules.