Dipartimento di Scienze, Università della Basilicata, Via dell'Ateneo Lucano 10, 85100 Potenza, Italy.
Photochem Photobiol Sci. 2019 Oct 9;18(10):2297-2362. doi: 10.1039/c9pp00148d.
The photochemical reaction between an excited state of carbonyl compounds and an alkene to give the oxetane deriving from a cycloaddition reaction (the Paternò-Büchi reaction) is presented. The mechanism of the reaction is discussed on the basis of kinetic, spectroscopic, and theoretical evidence, showing that the reaction can involve both singlet and triplet excited states of the carbonyl compounds, the high probable presence of an exciplex, and the possible presence of electron transfer processes, and when triplet excited carbonyl compounds are involved, the presence of a biradical intermediate is observed. The reactivity of electron-poor and electron-rich alkenes is discussed. Regio- and stereochemical behavior of the reaction are presented showing that, in some cases, very high regio- and stereoselectivities are obtained. The possible theories explaining this behavior are presented. In this field, the stereoselectivity observed, when chiral auxiliaries are used, when the reaction is performed in organized media, and when the presence of a hydroxyl directing effect can be supposed, is presented. The effect of light, temperature, solvent on the reaction is discussed. The possible application of this reaction in organic synthesis is discussed, presenting both previous synthetic schemes where the synthesis of an oxetane is a key step, the possible use of the oxetane in synthesis, and comparing the photochemical approach with the other approaches used to synthesize the oxetane ring.
羰基化合物的激发态与烯烃之间的光化学反应生成来自环加成反应（Paternò-Büchi 反应）的氧杂环丁烷。根据动力学、光谱和理论证据讨论了反应的机理，表明反应可以涉及羰基化合物的单重态和三重态激发态、高可能存在的激发复合物以及可能存在的电子转移过程，并且当涉及三重态激发羰基化合物时，观察到双自由基中间体的存在。讨论了缺电子和富电子烯烃的反应性。呈现了反应的区域和立体化学行为，表明在某些情况下，可获得非常高的区域和立体选择性。提出了可能解释这种行为的理论。在该领域中，当使用手性助剂、在组织化介质中进行反应以及可以假定存在羟基导向效应时，观察到的立体选择性，呈现了出来。讨论了光、温度、溶剂对反应的影响。讨论了该反应在有机合成中的可能应用，提出了之前的合成方案，其中氧杂环丁烷的合成是关键步骤，可能在合成中使用氧杂环丁烷，并比较了光化学方法与用于合成氧杂环丁烷环的其他方法。
