Reactivity of (<i>Z</i>)-4-Aryliden-5(4<i>H</i>)-thiazolones: [2 + 2]-Photocycloaddition, Ring-Opening Reactions, and Influence of the Lewis Acid BF<sub>3</sub>
作者:Sonia Sierra、David Dalmau、Sheila Higuera、Darío Cortés、Olga Crespo、Ana I. Jimenez、Alexandra Pop、Cristian Silvestru、Esteban P. Urriolabeitia
DOI:10.1021/acs.joc.1c01458
日期:2021.9.3
This reaction takes place with high stereoselectivity, given that the ε-isomer (1,3 head-to-tail syn coupling) is formed in more than 90% yield in most of the cases. However, irradiation of 5(4H)-thiazolones 2 with blue light (456 nm) in dry MeOH in the presence of BF3·OEt2 leads to the monospirocyclobutanes 4 with full stereoselectivity, also affording the ε-isomer. A ring-opening reaction of only
( Z )-2-苯基-4-亚芳基-5(4 H )-噻唑啉酮2在 CH 2 Cl 2溶液中用蓝光 (465 nm) 照射促进环外 C=C 的 [2 + 2]-光环加成键和二螺环丁烷的形成3 。该反应以高立体选择性发生,在大多数情况下,ε-异构体(1,3 头尾顺式偶联)的产率超过 90%。然而,在BF 3 ·OEt 2存在下,用蓝光(456 nm)在干燥MeOH中照射5(4 H )-噻唑啉酮2产生具有完全立体选择性的单螺环丁烷4 ,也提供ε-异构体。 4在甲醇解时似乎仅发生了一个噻唑酮环的开环反应,产生相应的酯和硫代酰胺基团。用醇中的碱 (NaOR/ROH) 处理游离的 4-亚芳基-5(4 H )-噻唑啉酮2也会通过甲醇解产生杂环的开环反应,尽管在这些反应条件下,进一步的分子内 S-观察到环外 C(H)=C 键的攻击并环化,形成具有高非对映异构体过量的顺式( RS / SR ) 和反式( RR