GROUND-STATES OF MOLECULES .68. MNDO STUDY OF THE CLAISEN REARRANGEMENT
GROUND-STATES OF MOLECULES .68. MNDO STUDY OF THE CLAISEN REARRANGEMENT
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DOI：
10.1021/ja00335a043
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发表时间：
1984-01-01
影响因子：
15
通讯作者：
HEALY, EF
中科院分区：
文献类型：
--
作者：
DEWAR, MJS;HEALY, EF
MNDO计算报告的克莱森重排3-氧杂-1-己烯，其各种甲氧基和氰基衍生物，并为2-甲氧基-5-氰基衍生物。发现该反应是通过两阶段机理发生的，类似于2，5-己二烯的Cope重排，但中间体biradicaloid不是稳定的物种，在没有活化的情况下转化为产物。结果与取代基效应的现有证据一致，并导致可验证的predictions.The术语“克莱森重排”最初被应用于重排烯丙基芳基醚邻位，或偶尔帕拉，苯酚，例如，1-* 2。近年来，它已扩展到包括烯丙基乙烯基醚到不饱和醛和酮的类似重排反应，如3- 4.2。后一种反应类似于1，5-己二烯（如5-* 6）的科普重排反应，其中一个饱和碳原子被氧取代，现在同样归类为[3，3] σ-迁移重排反应。3直到最近，人们一般认为这类反应是通过芳香族5，6过渡态（TS）以同步方式4发生的，该过渡态是由两个烯丙基部分中碳原子的2 p AO型和ir型重叠的组合形成的。正如Doering和Roth在不久前指出的那样，这样的TS原则上可以以类似于环己烷的椅型和船型构象的几何构型（7，8）存在。他们能够通过一个巧妙的实验表明，椅子TS（7）是有利的。类似的考虑适用于烯丙基乙烯基醚的克莱森重排，和施密特等人，8同样表明，这些也发生通过椅子型中间体，9。这一证据清楚地表明，这两种反应都不是通过裂变成自由基和再结合而发生的。在每种情况下，新CC键的形成必须在断裂CC（或CO）键完全断裂之前开始。
MNDO calculations are reported for the Claisen rearrangements of 3-oxa-l-hexene, for its various methoxy and cyano derivatives, and for the 2-methoxy-5-cyano derivative. Thereactions are found to take place by a two-stage mechanism, analogous to that of theCope rearrangement of 2, 5-hexadiene but where the intermediate biradicaloid is not a stable species, undergoing conversion to theproduct without activation. The results agree with the available evidence concerning substituent effects and lead to verifiable predictions.The term “Claisen rearrangement” was originally applied to rearrangements of allyl aryl ethers toortho, or occasionally para, phenols, eg, 1—* 2. In recentyears, however, it has been extended to include the analogous rearrangements of allyl vinyl ethers to unsaturated aldehydes and ketones, eg, 3— 4.2 The latter reactions are analogues of Cope rearrangements of 1, 5-hexadienes (eg, 5-* 6) in which one of the saturated carbon atoms is replaced by oxygen and are now likewise classed as [3, 3] sig-matropic rearrangements. 3 Until recently it was generally as-sumed that reactions of this kind take place in a synchronous4 manner, via aromatic5, 6 transition states (TS), formed by a com-bination of-type and ir-type overlap of the 2p AOs of the carbon atoms in the two allyl moieties. As Doering and Roth7 pointed out some time ago, such a TS can in principle exist in geometries (7, 8) analogous to those of the chair and boat conformers of cyclohexane. They were able to show by an ingenious experiment that the chair TS (7) is favored. Similar considerations apply to the Claisen rearrangements of allyl vinyl ethers, and Schmidt et al., 8 have likewise shown that these too take place via chair-type intermediates, 9. This evidence shows clearly that neither reaction takes place by fission into radicalsand recombination. In each case formation of the new CC bond must begin before the breaking CC (or CO) bond has completely broken.