Cycloaddition Chemistry of 1,3-Thiazolium-4-olate Systems. Reaction with Nitroalkenes and Interpretation of Results Using PM3 Calculations.
Cycloaddition Chemistry of 1,3-Thiazolium-4-olate Systems. Reaction with Nitroalkenes and Interpretation of Results Using PM3 Calculations.
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1,3-噻唑鎓-4-油酸盐体系的环加成化学。
DOI：
10.1002/chin.199639140
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
J. Palacios
中科院分区：
文献类型：
--
作者：
M. Ávalos;Reyes Babiano;Andrés Cabanillas;P. Cintas;F. Higes;J. Jiménez;J. Palacios
1，3-噻唑鎓-4-醇盐（容易由硫脲基衍生物制备）和反式-β-硝基苯乙烯在室温下在二氯甲烷中的1，3-偶极环加成（48 h）通过在这些反应条件下经历重排的瞬时环加合物产生两种容易分离的非对映体外消旋4，5-二氢噻吩。使用手性碳水化合物衍生的硝基烯烃，得到两个非对映异构体的二氢噻吩，表明区域特异性和面部选择性参与这些环加成。(1)H NMR数据和捕获实验与孤立的初始环加合物表明，环加成是可逆的，并占观察到的加合物和最终产物的比例。单晶X-射线测定建立的关键中间体和产品的结构，和PM 3半经验MO计算提供了一个合理化的噻唑-4-olates的反应性和在环加成中观察到的区域选择性。
1,3-Dipolar cycloaddition of 1,3-thiazolium-4-olates, readily prepared from thioureido derivatives, and trans-beta-nitrostyrene at room temperature in methylene chloride (48 h) resulted in two readily separable diastereomeric racemic 4,5-dihydrothiophenes via transient cycloadducts that underwent rearrangement under these reaction conditions. Using chiral carbohydrate-derived nitroalkenes, two diastereomeric dihydrothiophenes were obtained, showing that regiospecificity and facial selectivity were involved in these cycloadditions. (1)H NMR data and trapping experiments with isolated initial cycloadducts indicated that the cycloadditions were reversible and accounted for observed adduct and final product ratios. Single-crystal X-ray determinations established the structures of critical intermediates and products, and PM3 semiempirical MO calculations provide a rationalization for both the reactivity of the thiazolium-4-olates and the regioselectivity observed in the cycloadditions.