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Nucleophilic Carbonyl Addition of Organometallics: Reaction Pathway, Transition State Structure and Stereoselectivity

有机金属化合物的亲核羰基加成：反应途径、过渡态结构和立体选择性

基本信息

批准号：
03640451
负责人：
YAMATAKA Hiroshi
金额：
$ 1.28万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

Tow reaction routes are possible for nucleophilic additions to carbonyl compounds, polar addition and electron transfer-radical coupling sequence. We have demonstrated that a new radical anion probe experiment utilizing dehalogenation of halo-substituted benzophenone is effective to detect the occurrence of electron transfer during the reaction. Three reactions were carried out: the Grignard reactions, for which the electron transfer mechanism is highly recommended, the addition of allyltributyltin, the reaction considered to proceed through the polar mechanism, and the Wittig reaction for which the reaction pathway is not known at present. In the reaction of omicron-Br or I-benzophenone with MeMgl and PhMgBr considerable amount of dehalogenation products was observed, which clearly indicate the occurrence of electron transfer during the reaction. In contrast, a similar probe reaction with allyltributyltin was found negative. These two sets of reactions confirmed the usefulness of the new probe experiment to detect the occurrence of electron transfer during the reaction in question. Application of this new technique to the Wittig reaction then indicated that the reaction mechanism if highly dependent on the structure of ylide; the reactions of nonstabilized ylides proceed via electron transfer route while those of a semistabilized ylide go through the polar mechanism. These results are fully consistent with the isotope effect as well as the substituent effect data obtained last year in these Wittig reactions. The difference in the reaction route is considered to by responsible to the observed diversity in stereochemistry of the Wittig reaction.

羰基化合物的亲核加成反应有两种可能的反应路线：极性加成和电子转移-自由基偶合顺序。我们已经证明，一种新的自由基阴离子探针实验利用卤代二苯甲酮的脱卤是有效的，以检测在反应过程中发生的电子转移。进行了三个反应：Grignard反应，其中电子转移机制是高度推荐的，添加烯丙基三丁基锡，反应被认为是通过极性机制进行的，和Wittig反应，其中的反应途径目前还不知道。在Omicron-Br或I-二苯甲酮与MeMgl和PhMgBr的反应中观察到大量的脱卤产物，这清楚地表明在反应过程中发生了电子转移。相反，与烯丙基三丁基锡类似的探针反应被发现为阴性。这两组反应证实了新探针实验在检测所讨论的反应期间电子转移的发生方面的有用性。应用这种新技术的Wittig反应，然后表明，如果高度依赖于叶立德的结构的反应机理，不稳定的叶立德进行通过电子转移途径，而那些半稳定叶立德通过极性机制。这些结果与去年在这些Wittig反应中获得的同位素效应以及取代基效应数据完全一致。反应途径的差异被认为是导致观察到的维蒂希反应立体化学多样性的原因。