A novel unsymmetrical dibenzylidene acetone (monothiophos-dba, compound 3), containing two chemically different alkene moieties, undergoes a selective photochemically-induced [2+2] cycloaddition solid-state transformation (single crystal and powder), as shown by X-ray diffraction methods. In the single crystal the rate constant for the cycloaddition reaction was determined k = (2.3 ± 0.1) × 10−4 s−1}, with a 69% conversion attained, which compares well with a two-photon irradiation experiment using a Nd:YAG laser pumped dye laser at 605 nm radiation (66% conversion). Full conversion was attained using powdered 3 after 43 h. A similar conversion was noted between the single crystal and powder forms (59% and 66% conversion after 5 h irradiation). Irradiation of monothiophos-dba in solution using a 325 nm laser, and monitoring by 1H NMR spectroscopy, showed that no cycloaddition occurred, but exclusive photochemically-induced trans → cis isomerisation of the alkene bond connecting the unsubstituted aryl group (cis → trans isomerisation in these electron-deficient and polarised CC bonds occurs rapidly by thermal equilibration).
X 射线显示,一种新型不对称
二亚苄基丙酮(monothiophos-dba,化合物 3)含有两个
化学上不同的烯烃部分,会发生选择性光
化学诱导的 [2+2] 环加成固态转变(单晶和粉末)衍射方法。在单晶中,确定了环加成反应的速率常数 k = (2.3 ± 0.1) × 10−4 s−1},实现了 69% 的转化率,这与使用 Nd 的双光子辐照实验相比较:YAG 激光泵浦
染料激光,辐射波长为 605 nm(66% 转换率)。 43小时后使用粉末状3实现完全转化。在单晶和粉末形式之间注意到类似的转化(5小时照射后转化为59%和66%)。使用 325 nm 激光照射溶液中的单
硫磷-dba,并通过 1 H NMR 光谱监测,表明没有发生环加成,但仅发生光
化学诱导的连接未取代芳基的烯烃键的反式 → 顺式异构化(在这些缺电子和极化的 CC 键通过热平衡迅速发生)。