Design of new reactions using N-Heterocyclic carbenes as organocatalysts

n -杂环碳因其独特的性质引起了化学界的广泛关注。作为强大的电子供体，它们已迅速成为一类重要的过渡金属配体。此外，在没有过渡金属的情况下，它们也可以作为催化剂。大多数被NHCs加速的反应的共同特点是醛的正常反应性被逆转。这些官能团通常作为亲电试剂（电子受体）反应，在催化过程中变成亲核试剂（电子给体）。尽管具有这种反应性逆转的独特性质，但直到最近才将NHCs应用于数量迅速增加的迄今未知的反应中。我们在这一领域的努力主要集中在新的环扩张反应和由NHCs引发的多米诺反应的发展上。这一建议详述了我们在未来五年将追求的四个新方向。新的多米诺Diels-Alder和Stetter反应将基于反应性逆转的概念设计，并将开发更有效的催化剂。亲核催化，一种较少探索的NHCs反应模式也将被探索。这些进展将应用于生物活性天然产物及其类似物的合成。

Due to their unique properties, N-heterocyclic carbenes (NHCs) have attracted a lot of attention from the chemistry community. Being powerful electron donors, they have rapidly established themselves as an important class of ligands for transition metals. Moreover, they can also act as catalysts in the absence of transition metals. Common to most reactions that are accelerated by NHCs is the reversal of the normal reactivity of aldehydes. These functional groups, which usually react as electrophiles (electron-acceptors), become nucleophiles (electron-donors) in the catalyzed process. Despite this unique property of reactivity reversal, NHCs have only recently been applied to a rapidly increasing number of hitherto unknown reactions. Our own efforts in this area have focused on novel ring expansion reactions and on the development of domino reactions initiated by NHCs. This proposal details four new directions we will pursue over the next five years. New domino Diels-Alder and Stetter reactions will be designed based on the concept of reactivity reversal, and more efficient catalysts will be developed. Nucleophilic catalysis, a less-explored mode of reactivity for NHCs will also be explored. These advances will be applied to the synthesis of biologically active natural products and their analogues.