2,2,6,6-Tetramethylcyclohexanethione S-methylide, a highly hindered thiocarbonyl ylide: two-step cycloadditions
作者:Rolf Huisgen、Henry Giera、Kurt Polborn
DOI:10.1016/j.tet.2005.02.062
日期:2005.6
reactants. In contrast to previously studied models, the title compound 1C, a thiocarbonyl ylide prepared by N2 extrusion from dihydrothiadiazole 7C at 80 °C, combined with 2,3-bis(trifluoromethyl)fumaronitrile (11) to give a zwitterion (gauche-10); the latter failed to close the thiolane ring by 1,5-cyclization, but formed the seven-membered ketene imine 9C by 1,7-cyclization. X-ray analysis of 9C revealed
从两性离子的中间体从一致的1,3-偶极环加成转换为两步路径,需要1,3-偶极和偶极亲子的HOMO-LUMO能量之间的主要能量差,以及空间上需要的反应物。与以前研究的模型相反,标题化合物1C是在80°C下由N. 2从二氢噻二唑7C N 2挤出制备的硫代羰基内酯,与2,3-双(三氟甲基)富马腈(11)结合,得到两性离子(gauche - 10); 后者未能通过1,5-环化封闭硫杂环戊烷环,但通过1,7-环化形成了七元烯酮亚胺9C。9C的X射线分析揭示了一个角度变形的累积键系统和CF 3基团的Transoid关系。相对稳定的9C允许在-90至+90°C范围内进行19 F NMR记录;与温度相关的谱线加宽是由与≤1%的未知异构体平衡引起的。在各种可能的角度应变速率过程,反转transoid 19 ⇌ cisoid 20优选其涉及在CN键的topomerization; 讨论了横向反转和旋转。在溶液
1,2-Bis(trifluoromethyl)ethene-1,2-dicarbonitrile: Enol Ethers and Ketene Acetals as Cycloaddition Partners
作者:Rolf Huisgen、Gonzalo Urrutia Desmaison
DOI:10.1002/hlca.201200217
日期:2012.7
19F‐NMR data served the structural assignment and the quantitative analysis. The mechanistic discussion is based on rotations and ring closures of the assumed 1,4‐zwitterionic intermediates. Dimethylketene dimethyl acetal, methylketene dimethyl acetal, and ketene diethyl acetal show an increasing rate in their reactions with BTE as well as in the equilibration of the cycloadducts.
to vinyl ether, the pathways leading to mono‐ and bis‐adducts must compete on the level of the intermediate l,4‐zwitterions 1 and 2. The latter either cyclize to the cyclobutanes 3 or to six‐membered cyclic ketene imines 8 which accept a second molecule of vinyl ether to yield the bis‐adducts 6. The occurrence of the highly strained ketene imines 8 gains credibility by comparison to stable seven‐membered
equilibrate with nucleophilic catalysts. Both undergo (2+2) cycloadditions with methyl vinylether at 25°. Three stereogenic centers in the cyclobutanes led to four rac‐diastereoisomers, which were obtained in pure and crystalline state. The structures were elucidated by 19F‐NMR spectroscopy and confirmed by two X‐ray analyses. The cycloadditions were not stereospecific: e.g., (E)‐BTE furnished 73% trans‐adducts
hanide (2), which cannot be isolated but is interceptible by dipolarophiles, is set free. The nucleophilic 1,3-dipole 2 undergoes cycloadditions with electrophilic C,C multiplebonds; the structures of 16 cycloadducts were elucidated. One-step and two-step cycloaddition pathways are discussed in the light of the steric course observed for (E)/(Z)-isomeric ethylene derivatives. Competition experiments