定义Definition
帕特诺-比希反应是光激发的羰基化合物与烯烃发生 [2+2] 环加成，生成四元含氧环（氧杂环丁烷）的光化学反应。
The Paternò–Büchi reaction is a photochemical [2+2] cycloaddition of an excited carbonyl compound with an alkene that forms a four-membered oxygen heterocycle, an oxetane.
机理Mechanism
羰基吸收紫外光发生 n→π* 激发，常经系间窜越成三线态。激发态羰基的氧进攻烯烃形成 1,4-双自由基中间体，自旋翻转后闭环成氧杂环丁烷。双自由基的相对稳定性决定区域选择性。
The carbonyl absorbs UV light (n→π*) and usually crosses to the triplet. The excited oxygen attacks the alkene to give a 1,4-biradical, which closes to the oxetane after spin inversion. The relative stability of possible biradicals controls regioselectivity.
由来Origin
意大利化学家埃马努埃莱·帕特诺于 1909 年首先报道苯甲醛与 2-甲基-2-丁烯在日光下的反应；1954 年美国化学家乔治·比希确定了产物的氧杂环丁烷结构。
The Italian chemist Emanuele Paternò first reported the sunlight reaction of benzaldehyde with 2-methyl-2-butene in 1909; in 1954 the American chemist George Büchi established the oxetane structure of the product.
意义Significance
热条件下 [2+2] 是轨道对称禁阻的，光化学条件下则被允许，该反应是伍德沃德-霍夫曼规则的典型例子，也是合成氧杂环丁烷的重要方法。
A thermal [2+2] is symmetry-forbidden but the photochemical version is allowed, making this reaction a textbook illustration of the Woodward–Hoffmann rules and an important route to oxetanes.
反应Reactions
紫外光照射，常在苯或乙腈中
UV irradiation, often in benzene or acetonitrile
羰基 n→π* 激发并系间窜越到三线态。
n→π* excitation of the carbonyl and intersystem crossing to the triplet.
氧原子加到烯烃上形成 1,4-双自由基。
The oxygen adds to the alkene to form a 1,4-biradical.
自旋翻转后自由基偶合闭环。
After spin inversion the radicals combine to close the ring.
帕特诺最早研究的体系。
Paternò's original system.
年表Timeline
- 1909
帕特诺报道该光反应
Paternò reports the photoreaction
- 1954
比希确定氧杂环丁烷结构
Büchi establishes the oxetane structure