Reactions of a sterically hindered tetrasubstituted thiocarbonyl ylide with acceptor-substituted ethylenes; regioselectivity and stereochemistry
作者:Grzegorz Mloston、Rolf Huisgen、Henry Giera
DOI:10.1016/s0040-4020(02)00384-8
日期:2002.5
The 1,3-cycloadditions of the tetra-substituted thiocarbonyl ylide 8, set free by N2 extrusion from thiadiazoline 7, with methyl acrylate and acrylonitrile furnish 3′-and 4′-substituted thiolanes, probably by a concerted pathway. In the reactions of 8 with dimethyl 2,3-dicyanofumarate (27) and dimethyl 2,3-dicyanomaleate (28), zwitterionic intermediates, which are capable of conformational rotation
通过从噻二唑啉7中的N 2挤出而释放的四取代的硫代羰基内酯8的1,3-环加成物可能与丙烯酸甲酯和丙烯腈一起提供3′-和4′-取代的硫杂环戊烷,可能是通过协同途径。在8与2,3-二氰基富马酸二甲酯(27)和2,3-二氰基苹果酸二甲酯(28)的反应中,能够构象旋转的两性离子中间体位于两个不可逆反应的分支点:环化成硫氰酸根23 / 24和片段化至环丙烷31 / 32加硫酮12。两种反应都伴随着一些立体化学纯度的损失。对于环丙烷形成两种机制进行了讨论:分子内亲核取代在抗-zwitterions 29日/ 30或无辅助heterolysis导致叔-carbenium两性离子作为另外的中间。