Enantioselective Catalysis of [2+2] Photocycloaddition Reactions

[2+2]光环加成反应是有机化学中最重要的光诱导反应（光化学反应）。该反应的产物为环丁烷，具有广泛的手性和潜在的合成应用。对手性化合物的单一对映体形式的选择性接触称为对映选择反应。本项目的目标是寻找手性催化剂，允许在[2+2]光环加成反应中对映选择性制备环丁烷。由于光化学反应即使在没有催化剂的情况下也能在激发下快速进行，因此需要与经典催化不同的新概念。将底物-催化剂结合的过程与选择性光吸收结合起来，并通过这样做来确保底物激发只可能在催化剂的手性环境中发生，这似乎特别有前途。为此，一种提出的方法是基于[2+2]光环加成底物在酸（Lewis或Brønsted酸）或某些中间体（铵离子或胺）的配合物中表现出长波吸收这一事实，这引起了选择性激发。另一种方法旨在开发具有催化活性的手性增敏剂，并在底物-增敏剂复合物内选择性地转移能量。

The [2+2] photocycloaddition is the most important light-induced reaction (photochemical reaction) of organic chemistry. The products of the reaction are cyclobutanes, which possess great potential for possible synthetic applications and which are in general chiral. The selective access to a single enantiomeric form of a chiral compound is called an enantioselective reaction. The goal of the present project is to find chiral catalysts that allow for the enantioselective preparation of cyclobutanes in a [2+2] photocycloaddition reaction. Due to the fact that photochemical reactions proceed upon excitation ¿ even in the absence of a catalyst ¿ very rapidly, novel concepts are required, which are different from those of classical catalysis. It appears particularly promising to combine the process of substrate-catalyst binding with selective light absorption and ¿ by doing so ¿ to ensure that substrate excitation is only possible in the chiral environment of the catalyst. To this end, one proposed approach is based on the fact that [2+2] photocycloaddition substrates exhibit a long-wavelength absorption in complexes with acids (Lewis or Brønsted acids) or in certain intermediates (onium ions or enamines), which invites selective excitation. The other approach aims to develop chiral sensitizers that are catalytically active and that transfer energy selectively within a substrate-sensitizer complex.