Cycloadditions of two thiocarbonyl ylides with α,β-unsaturated esters and nitriles: steric course and mechanism
作者:Rolf Huisgen、Grzegorz Mloston、Henry Giera、Elke Langhals
DOI:10.1016/s0040-4020(01)01147-4
日期:2002.1
In the probably concerted cycloadditions of the sterically hindered thiocarbonyl ylide 1 with fumaronitrile, maleonitrile, and dimethyl fumarate, the dipolarophile configuration is retained whereas retention/inversion 99:1 for dimethyl maleate (51 times less reactive than fumarate) signals a small involvement of a two-step pathway. The latter becomes dominant when two acceptor groups stabilize the
在空间受阻的硫代羰基内酯1与富马腈,顺丁烯二腈和富马酸二甲酯的可能协同加成反应中,保留了双极性亲和性构型,而马来酸二甲酯的保留/转化率为99:1(比富马酸酯低51倍)表明甲酰胺的少量参与。两步走法。当两个受体基团稳定两性离子中间体的阴离子末端时,后者就占主导地位。的环加成Nonstereospecific 1用二甲基-2,3- dicyanofumarate(16,保留/反转60:40)和二甲基2,3- dicyanomaleate(17观察,76:24)。需要特殊条件以避免前面的顺式,反式异构化,16 ⇄ 17,由噻二唑啉催化4,的前体1。在相关的硫代羰基叶立德37的情况下,这种催化作用无法被抑制,并且与16和17的加合物比例相同(55:45)。