Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & School of Future Technology, University of CAS, the Chinese Academy of Sciences, Beijing, China.
Photochem Photobiol. 2019 Jan;95(1):24-32. doi: 10.1111/php.12993. Epub 2018 Sep 28.
Enantioselectivity in organic transformations continues to be a topic major interest in organic photochemistry. In the last decade, synergistic combination of photocatalysis and organocatalysis has emerged as a powerful strategy to gain enantioselectivity in photochemical reactions, and remarkable achievements have been obtained. In this strategy, the asymmetric induction is provided in ground state. In contrast, in the conventional enantioselective photochemistry, the chiral induction is controlled in electronic excited state, and to achieve high stereoselectivity is still a formidable challenge. Because the reactions of excited states often yield strained products with unique structures in single step that are difficult to form by thermal reactions, the development of new strategies attempted to achieve enantioselectivity in excited state reactions is still highly desired. Since the short excited state lifetime and low activation energy for reaction in excited state leave little room for manipulating the chiral induction, in order to gain enantioselectivity the substrate molecule has to already reside in a chiral environment during the excitation step. Chiral auxiliaries and chiral supramolecular hosts can provide such environments. In this presentation, we summarize the studies employing chiral auxiliary and chiral microreactor approaches to achieve high asymmetric inductions in excited state reactions performed in our laboratory. We chose the photodimerization of alkyl 2-naphthoates as a reaction model to give deeper insights into the basic factors controlling chiral induction in excited state.
对映选择性在有机转化中仍然是有机光化学的一个主要研究课题。在过去的十年中，光催化和有机催化的协同结合已成为获得光化学反应对映选择性的一种强大策略，并取得了显著的成果。在该策略中，不对称诱导发生在基态。相比之下，在传统的对映选择性光化学中，手性诱导受电子激发态控制，要实现高立体选择性仍然是一个巨大的挑战。由于激发态的反应通常会生成一步生成具有独特结构的应变产物，这些产物很难通过热反应形成，因此，开发新的策略试图在激发态反应中实现对映选择性仍然是非常需要的。由于激发态的短寿命和反应的低活化能使得手性诱导的操纵空间很小，为了获得对映选择性，底物分子在激发步骤中就必须已经处于手性环境中。手性助剂和手性超分子主体可以提供这样的环境。在本次演讲中，我们总结了我们实验室采用手性辅助剂和手性微反应器方法在激发态反应中实现高不对称诱导的研究。我们选择烷基 2-萘酸酯的光二聚化为反应模型，以更深入地了解控制激发态手性诱导的基本因素。
