School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, People's Republic of China.
Acc Chem Res. 2012 Oct 16;45(10):1736-48. doi: 10.1021/ar3000508. Epub 2012 Jul 27.
Oxidation reactions are central components of organic chemistry, and modern organic synthesis increasingly requires selective and mild oxidation methods. Although researchers have developed new organic oxidation methods in recent years, the chemistry community faces continuing challenges to use "green" reagents and maximize atom economy. Undoubtedly, with its low cost and lack of environmentally hazardous byproducts, molecular oxygen (O(2)) is an ideal oxidant. However, relatively limited methodologies are available that use O(2) efficiently in selective organic transformations. Recently, the use of metal catalysts coupled with the reduction of O(2) has become an attractive approach for aerobic oxidation. In particular, Pd complexes have shown great potential for the development of versatile aerobic reactions because of their ability to directly couple O(2) reduction. As a result, these complexes have attracted tremendous research attention and afford new opportunities for selective oxidation chemistry. In this Account we highlight some of our progress toward the synthetic goal to functionalize the unsaturated hydrocarbons largely through the appropriate choice of Pd catalysts and O(2). We have focused on developing simple and efficient methods to construct new carbon-carbon and carbon-heteroatom bonds with O(2) as the oxidant and/or reactant. We have demonstrated Pd-catalyzed oxidation of carbon-carbon double bonds, Pd-catalyzed oxidation of carbon-carbon triple bonds, and Pd-catalyzed oxidative cross-coupling reactions of alkenes and/or alkynes with high selectivity. O(2) plays a critical role in the success of these transformations. Most of the reactions can tolerate a range of functional groups, and some can occur under aqueous conditions. Depending on the specific process, we propose several mechanistic scenarios that describe the in situ generation of different intermediates and discuss the plausible reaction pathways. These methods provide new strategies for the green synthesis of diverse 1,2-diols, carbonyls, lactones, conjugated dienes, trienes, and aromatic rings. These products have potential applications in natural product synthesis, materials science, and bioorganic chemistry. Given our new mechanistic understanding, we are optimistic that additional Pd-catalyzed aerobic oxidative transformations will be developed that are both more economical and environmentally friendly.
氧化反应是有机化学的核心组成部分，现代有机合成越来越需要选择性和温和的氧化方法。尽管近年来研究人员开发了新的有机氧化方法，但化学界仍然面临着使用“绿色”试剂和最大限度地提高原子经济性的挑战。毫无疑问，氧气（O(2)）具有成本低且无环境危害副产物的特点，是一种理想的氧化剂。然而，能够高效地将氧气用于选择性有机转化的方法相对有限。最近，使用金属催化剂结合氧气还原已成为有氧氧化的一种有吸引力的方法。特别是，钯配合物因其能够直接偶联氧气还原而显示出开发多功能有氧反应的巨大潜力。因此，这些配合物引起了人们极大的研究关注，并为选择性氧化化学提供了新的机会。在本综述中，我们重点介绍了我们在通过适当选择钯催化剂和氧气来实现不饱和烃功能化的合成目标方面的一些进展。我们专注于开发简单有效的方法，用氧气作为氧化剂和/或反应物构建新的碳-碳和碳-杂原子键。我们已经证明了钯催化的碳-碳双键氧化、碳-碳三键氧化以及烯烃和/或炔烃的钯催化氧化交叉偶联反应具有高选择性。氧气在这些转化的成功中起着关键作用。大多数反应可以耐受一系列官能团，有些反应可以在水相条件下进行。根据具体的过程，我们提出了几种描述不同中间体原位生成的机理情景，并讨论了可能的反应途径。这些方法为各种 1,2-二醇、羰基化合物、内酯、共轭二烯、三烯和芳环的绿色合成提供了新的策略。这些产物在天然产物合成、材料科学和生物有机化学中有潜在的应用。鉴于我们对新的机理理解，我们乐观地认为，将开发出更经济、更环保的钯催化有氧氧化转化。
