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Reaction Route of Nucleophilic Addition to Carbonyl Compounds : Intermediate, Transition State and Selectivity

羰基化合物亲核加成反应路线：中间体、过渡态和选择性

基本信息

批准号：
07454167
负责人：
YAMATAKA Hiroshi
金额：
$ 5.06万
依托单位：
Osaka University (1996)Kyushu University (1995)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

A carbonyl addition reaction, in general, proceeds by way of either a polar direct nucleophilic attack in one step or a two-step process going through a radical ion intermediate. In this project, the mechanism of the addition reaction of a series of nucleophlies including Wittig reagents and organolithium reagents (MeLi.PhLi, CH_2=CHCH_2Li, PhSCH_2Li, LiCH_2CN,and (CH_3) _3CCH_2C (OLi) =CH_2) with benzophenone and benzaldehyde. As for the organilithium reagents, it was found that the reaction of lithium pinacolone enolate with benzaldehyde goes through the polar mechansim whereas the reactions of other Li reagets with benzaldehyde and benzophenone proceed via the rate-determining electron transfer mechanism. The mechanistic difference correlates with the stability of the reagents measured by the intrinsic acidity of the conjugative acids of R anions in the gas phase. The intrinsic acidity of R-H can be estimated from the gas phase heat of formation from the data compiled in the literature : 416.8kcal/mol (R=Me), 400.8 (Ph), 390.8 (CH_2=CHCH_2), 381.6 (PhSCH_2), 372.8 (NCCH_2), and 368.0 ((CH_3) _3CC (=O) CH_2). The enolate reagent whose conjugate acids the most acidic reacts with benzaldehyde via the polar mechanism whereas the reagents whose conjugate acids are less acidic go through the ET process. It is thus implied that the rate of the ET step depends more on the reactivity of a nucleophile than the rate of the PL step and that the crossing points is in between cyanomethyllithium and lithium pinacolone enolate for the reaction of the present series of the reagents with benzaldehyde.

羰基加成反应通常通过一步极性直接亲核攻击或通过自由基离子中间体的两步法进行。本课题研究了Wittig试剂、有机锂试剂（MeLi、PhLi、CH_2=CHCH_2Li、PhSCH_2Li、LiCH_2CN和（CH_3）_3CCH_2C（OLi）=CH_2）与二苯甲酮和苯甲醛的加成反应机理。在有机锂试剂中，烯醇式片那酮锂与苯甲醛的反应是通过极性机理进行的，而其它锂试剂与苯甲醛和二苯甲酮的反应则是通过速率控制电子转移机理进行的。的机制差异与试剂的稳定性相关的R阴离子在气相中的共轭酸的固有酸度测量。根据文献中的数据，由气相生成热估算R-H的本征酸性：416.8kcal/mol（R=Me），400.8（Ph），390.8（CH_2=CHCH_2），381.6（PhSCH_2），372.8（NCCH_2），368.0（（CH_3）_3CC（=O）CH_2）。共轭酸酸性最强的烯醇化物试剂通过极性机制与苯甲醛反应，而共轭酸酸性较低的试剂则通过ET过程。因此，这意味着ET步骤的速率比PL步骤的速率更多地取决于亲核试剂的反应性，并且对于本系列试剂与苯甲醛的反应，交叉点在氰基甲基锂和频哪酮烯醇化锂之间。