Reductive Coupling Reactions: Trading Organometallic Reagents for Organic Halides

催化C-C键形成反应已经彻底改变了学术界和工业界小分子的发现和合成，但是过渡金属催化的全部潜力现在经常受到对预形成的有机金属试剂的需求的限制。很少有这样的试剂是可商购的，因为它们的合成并不简单，并且许多试剂具有有限的稳定性。这些限制对药物发现和生物化学产生了影响，因为许多潜在的重要分子在被认为太耗时而无法获得时无法制造。这个问题的一个潜在的解决方案是用亲电子试剂，如有机卤化物，取代亲核有机金属试剂，其是工作台稳定的和丰富的。该计划的长期目标是开发新的催化反应，耦合两个或两个以上的亲电试剂，以及在这些还原偶联反应中控制选择性和反应性的因素的照明。在拟议的资助中，将为两种最重要的C-C键形成反应：交叉偶联和共轭加成开发还原替代方案。这项工作的指导机制假设是，第一行过渡金属的单电子化学将通过允许在单个金属中心发生多个氧化加成来实现两个亲电体的偶联。虽然自由基中间体几乎肯定会参与，但这些过渡金属催化的反应可以通过选择金属和配体来调节。因此，所开发的反应将为更好地研究其他金属的双电子过程提供补充反应性。根据强有力的初步数据，该提案的具体目标是：（1）开发从简单有机卤化物或拟卤化物形成Csp 3-Csp 2键的直接还原交叉偶联反应，并更好地理解转化机制;（2）创建形成Csp 3-Csp 3键的直接还原偶联方法;和（3）将还原偶联的概念扩展到包括有机卤化物与一氧化碳、烯烃和炔烃的偶联。在每一个目标下，在申请人的实验室中已经发现了一种有前途的催化剂体系，该体系将成为开发几种通用方法的基础。该方法是创新的，因为它专注于开发完全避免中间体有机金属试剂的新反应。已经确定了克服交叉选择性和反应性挑战的策略，这些策略以前阻碍了进展。通过研究具有不同机制的反应，拟议的研究为关键的C-C键形成反应以及以前不可能的新键结构的显着改进提供了机会。这项拟议中的研究意义重大，因为它有望扩大可以从商业可用材料快速制造的分子数量。从长远来看，这种易于获得的分子多样性的扩展将使分子生物学和药理学的发现能够直接影响人类健康。 公共卫生相关性：本申请中提出的新偶联反应不需要专门的技术或排除空气，使健康科学领域的人员，即使是化学经验有限的人员，也能够自己合成所需的分子。这项拟议中的研究与公共卫生和NIH的使命有关，因为正是从这个扩大的、多样化的库中，将发现明天的药物和分子探针。

DESCRIPTION (provided by applicant): Catalytic C-C bond forming reactions have revolutionized the discovery and synthesis of small molecules in academia and industry, but the full potential of transition-metal catalysis is now frequently limited by the need for pre-formed organometallic reagents. Few such reagents are commercially available because their synthesis is not trivial and many of the reagents have limited stability. These limitations have consequences for drug discovery and biochemistry because many potentially important molecules are not made when they are deemed too time consuming to access. One potential solution to this problem is the replacement of nucleophilic organometallic reagents with electrophiles, such as organic halides, which are bench stable and plentiful. This program's long-term goals are the development of new catalytic reactions that couple two or more electrophiles as well as the illumination of the factors which control selectivity and reactivity in these reductive coupling reactions. In the proposed grant, reductive alternatives will be developed for two of the most important types of C-C bond forming reactions: cross-coupling and conjugate addition. The guiding mechanistic hypothesis for this work is that the single-electron chemistry of first-row transition metals will enable the coupling of two electrophiles by allowing multiple oxidative additions to occur at a single metal center. Although radical intermediates are almost certainly involved, these transition-metal catalyzed reactions can be tuned through choice of metal and ligand. Thus, the reactions developed will provide a complementary reactivity to the better studied two-electron processes of other metals. Following up on strong preliminary data, the specific aims of the proposal are to: (1) develop direct reductive cross-coupling reactions that form Csp3- Csp2 bonds from simple organic halides or pseudohalides and better understand the mechanism of the transformation; (2) create direct reductive coupling methods that form Csp3-Csp3 bonds; and, (3) extend the concept of reductive coupling to include the coupling of organic halides with carbon monoxide, alkenes, and alkynes. Under each aim a promising catalyst system has been discovered in the applicant's laboratory that will become the basis for the development of several general methods. The approach is innovative because it focuses on the development of new reactions that completely avoid intermediate organometallic reagents. Strategies to overcome the challenges of cross-selectivity and reactivity have been identified that have previously prevented progress. By investigating reactions with different mechanisms, the proposed research presents the opportunity for dramatic improvements in critical C-C bond-forming reactions as well as new bond constructions that were not previously possible. The proposed research is significant because it is expected to expand the number of molecules that can be rapidly made from commercially available materials. In the long run, this expansion of readily accessible molecular diversity will enable discoveries in molecular biology and pharmacology that will directly impact human health. PUBLIC HEALTH RELEVANCE: The new coupling reactions proposed in this application do not require specialized techniques or the exclusion of air, empowering those in the health sciences, even those with limited chemistry experience, to synthesize needed molecules themselves. The proposed research is relevant to public health and the mission of the NIH because it is from this expanded, diversified pool that tomorrow's drugs and molecular probes will be discovered.