1,2-Bis(trifluoromethyl)ethene-1,2-dicarbonitrile: (2+2) Cycloadditions with Vinyl Ethers
作者:Gonzalo Urrutia-Desmaison、Rolf Huisgen、Heinrich Nöth
DOI:10.1002/hlca.201100449
日期:2012.1
equilibrate with nucleophilic catalysts. Both undergo (2+2) cycloadditions with methyl vinyl ether 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
标题化合物(简称BTE)存在于(E)和(Z)异构体中(两者的bp约为100°),它们与亲核催化剂平衡。两者都在25°与甲基乙烯基醚进行(2 + 2)环加成。环丁烷中的三个立体异构中心产生了四种rac-非对映异构体,它们以纯净和结晶状态获得。通过19 F-NMR光谱对结构进行了阐明,并通过两次X射线分析对其进行了确认。环加成不是立体特异性的:例如,(E)-BTE提供了73%的反式加合物(相对于CF 3组)和27%的顺式加合物。立体化学完整性的损失发生在中间笨拙-zwitterions这可环化或旋转,但不能解离。在极端条件下(2中号的LiClO 4的Et 2 O,70℃,3个月),四环丁烷的热力学平衡达到。两性离子中间体中的库仑吸引和构象应变的考虑使我们能够合理化所观察到的非对映异构体环丁烷的比例。乙基乙烯基醚和丁基乙烯基醚以相似的非对映异构体比率提供环丁烷。