CASSCF 分子轨道计算揭示了 [3,3] 硅重排反应的纯拟周环机制。

CASSCF molecular orbital calculations reveal a purely pseudopericyclic mechanism for a [3,3] sigmatropic rearrangement.

机构信息

Department of Chemistry, Lewis & Clark College, Portland, Oregon 97219-7899, USA.

出版信息

J Am Chem Soc. 2010 Feb 24;132(7):2196-201. doi: 10.1021/ja906679g.

PMID:20112898

Abstract

A comparative CASSCF/6-31G*-level computational study of the concerted [3,3] sigmatropic rearrangements of cis-1-iminyl-2-ketenylcyclopropane (15), cis-1-iminyl-2-propadienylcyclopropane (17), and cis-1-iminyl-2-keteniminylcyclopropane (19) to give products 16, 18, and 20, respectively, was conducted. Analysis of the active space MOs of TS(15-->16), TS(17-->18), and TS(19-->20) suggests that the 17 --> 18 and 19 --> 20 rearrangements are classically pericyclic, whereas the 15 --> 16 rearrangement is pseudopericyclic with two orbital disconnections-one involving the nitrogen lone-pair orbital and the other the carbonyl carbon of the ketene moiety. The novel TS(15-->16) was also found to have a highly planar, tight, geometry, whereas TS(17-->18) and TS(19-->20) were both shown to have the boat-shaped geometry expected for classically pericyclic [3,3] sigmatropic rearrangements. Results of calculations on the [3,3] sigmatropic rearrangements involving additional transition structures, TS(21-->22), TS(23-->24), TS(25-->26), TS(27-->28), TS(29-->30), and TS(31-->32), demonstrate the relative uniqueness of the pseudopericyclic one, TS(15-->16).

摘要

对顺式-1-亚氨基-2-烯基环丙烷（15）、顺式-1-亚氨基-2-丙二烯基环丙烷（17）和顺式-1-亚氨基-2-烯基甲亚胺基环丙烷（19）进行协同[3,3]σ重排生成产物 16、18 和 20 的 CASSCF/6-31G*-水平的比较计算研究。对 TS(15-->16)、TS(17-->18)和 TS(19-->20)的活性空间 MOs 的分析表明，17-->18 和 19-->20 重排是经典的周环反应，而 15-->16 重排是具有两个轨道切断的拟周环反应，一个涉及氮孤对轨道，另一个涉及羰基碳的烯酮部分。还发现新颖的 TS(15-->16)具有高度平面、紧密的几何形状，而 TS(17-->18)和 TS(19-->20)都具有经典周环[3,3]σ重排所预期的船形几何形状。对涉及额外过渡态 TS(21-->22)、TS(23-->24)、TS(25-->26)、TS(27-->28)、TS(29-->30)和 TS(31-->32)的[3,3]σ重排的计算结果表明，拟周环的独特性相对较高，TS(15-->16)。