Effects of an Electron-Withdrawing Group on Thermal Decomposition of 4-Alkylidene-1-pyrazolines: A Novel Stereoselective Formation of Alkylidenecyclopropane Due to Participation of π-Electrons on the Methylene Carbon in Decomposition
作者:Masashi Hamaguchi、Masahiro Nakaishi、Toshikazu Nagai、Hatsue Tamura
DOI:10.1021/jo035321i
日期:2003.12.1
es 7 arising from the bond formation between the exo-methylene carbon and the 5-carbon. The selective formation and the configurations of the products are rationalized in terms of the concerted process via the folded conformation of the pyrazolines. Introduction of an electron-withdrawing group at the 3-position of the 4-alkylidenepyrazoline system causes the polarization of the C(3)-N(2) bond inducing
进行了在C-3上带有甲氧基羰基的4-亚烷基吡唑啉14的热分解,该分解是通过在烯丙基羧酸酯12和重氮烷烃13之间进行1,3-偶极环加成而制备的。与普通的4-亚烷基吡唑啉在高温下会逐步分解的情况不同,14在中度低温(45-110摄氏度)下会协同分解,从而导致两个异构亚烷基间环丙烷7的选择性形成,这是由外-亚甲基之间的键形成引起的。碳和5碳。通过吡唑啉的折叠构象,在一致的工艺方面使产物的选择性形成和构型合理化。在4-亚烷基萘并吡唑啉系统的3位引入吸电子基团引起C(3)-N(2)键的极化,诱导分子内重氮盐8的性质,其中π电子在亚甲基碳变得更具亲核性,并参与C(5)-N(1)键的裂解。确定了在取代基之间仅具有小的空间相互作用的典型的正烷基亚烷基吡唑啉14a的X射线晶体结构为近似平面的环结构。