THE VINYLOGOUS ANOMERIC EFFECT IN 3-ALKYL-2-CHLOROCYCLOHEXANONE OXIMES AND OXIME ETHERS
THE VINYLOGOUS ANOMERIC EFFECT IN 3-ALKYL-2-CHLOROCYCLOHEXANONE OXIMES AND OXIME ETHERS
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DOI：
10.1021/ja00165a034
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发表时间：
1990-04-25
影响因子：
15
通讯作者：
JACOBS, RT
中科院分区：
文献类型：
--
作者：
DENMARK, SE;DAPPEN, MS;JACOBS, RT
一系列的z/w…已经制备了1 -3-烷基-2-氯代环己酮2（甲基、乙基、异丙基和叔丁基），并且显示除了优选twist-boat的叔丁基衍生物之外，其主要以双赤道椅型构象存在。形成的肟和各种肟衍生物（甲基肟，甲硅烷基肟）的结果在一个显着的构象反转的甲基，乙基和异丙基系统。通过对邻位质子间耦合常数的分析，认为这些化合物主要以双轴椅式构象存在。这通过（E）-trans-Sa的X射线晶体结构证实，其显示具有双轴取代基的椅子在固态下确实是优选的。一个强大的超共轭稳定的轴向构象被认为是这种偏好的起源，这被称为乙烯基异头效应，异头效应（及其广义表现形式）是很好的方案I公认为一个重要的贡献者的基态构象分析含杂原子系统。1在反应机理中考虑这些相同的效应（动力学异头效应2）的价值也得到了充分的证明。虽然
A series of z/w¡ j-3-alkyl-2-chlorocyclohexanones, 2 (methyl, ethyl, isopropyl, and zerz-butyl), have been prepared and shown to exist predominantly in the diequatorialchair conformation except the zert-butyl derivative which prefers a twist-boat. Formation of the oximes and various oxime derivatives (methyloxime, silyloxime) results in a remarkable conformational inversion for the methyl, ethyl, and isopropyl systems. By analysis of vicinal interproton coupling constants it is believed that these compounds exist predominantly in the diaxial chair conformation. This is corroborated by an X-ray crystal structure of (E)-trans-Sa which shows that the chair with diaxial substituents is indeed preferred in the solid state. A strong hyperconjugative stabilization of the axial conformation is proposed to be the origin of this preference which is termed the vinylogous anomeric effect.The anomeric effect (and its generalized manifestations) is well Scheme I recognized as an important contributor to ground-state conformational analysis of heteroatom-containing systems. 1 The value of considering these same effects in reaction mechanisms (kinetic anomeric effect2) has also been amply demonstrated. Although