Studies on the Mechanism of the [3+2] Annulation Based on the Brook Rearrangement

基于Brook重排的[3 2]成环机制研究

基本信息

批准号：
08672416
负责人：
TAKEDA Kei
金额：
$ 1.41万
依托单位：
TOYAMA MEDICAL AND PHARMACEUTICAL UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

Product distributions in the reactions of beta-heteroatom-substituted acryloylsilanes with ketone enolates, which was used in [3+2] annulation for preparation of functionalized cyclopentenols, highly depend upon the beta-substituent. Thus, in contrast to the observation with (E)- and (Z)-beta-phenylthio derivatives in which isomeric cyclopentenols were obtained in almost same ratio irrespective of the acylsilane geometry, the trimethylsilyl derivative afforded a single cyclopentenol and uncyclized enolsilyl ether in the ratio depending on the vinylsilane geometry. In order to rationalize these results, we postulated a reaction course which involves two compet-ing pathways depending of the alpha-carbanion-stabilizing ability of the beta-substituents in the acryloylsilane ; (a) intramolecular aldol reaction of delocalized allylic anion in termediate, Brook rearrangement product of 1,2-adduct, and (b) oxyanion-accelerated vinylcyclopropane rearrangement of cylcopropanolate which is derived from the 1,2-adduct via Brook rearrangement/cyclopropanation sequence. To get support to this proposal, we compared alpha-carbanion-stabilizing ability of the phenythio and the trimethylsilyl groups using the reactions of the acryloylsilanes with lithium enolate to t-butyl acetate, providing 1,2-addition product and Brook rearrangement/allylic rearrangement product in the ratio reflecting the difference of alpha-carbanion stabilizing ability of the b-substituent. And we examined low-temperature oxyanion accelerated vinylcyclo-propane-cyclopentene rearrangement using the reaction of four isomeric vinylcyclopropyl acetates with MeLi (2.2eq), affording the cyclopentenol and the uncyclized enol silyl ether in the ratio depending on the vinylsilane geometry.

β-杂原子取代的丙烯酰基硅烷与酮烯醇化物（用于[3+2]环化以制备官能化环戊烯醇）的反应中的产物分布高度依赖于β-取代基。因此，与(E)-和(Z)-β-苯硫基衍生物的观察相反，其中无论酰基硅烷的几何形状如何，都以几乎相同的比例获得异构环戊烯醇，三甲基甲硅烷基衍生物在比例取决于乙烯基硅烷的几何形状。为了使这些结果合理化，我们假设了一个反应过程，其中涉及两个竞争途径，具体取决于丙烯酰硅烷中β-取代基的α-碳负离子稳定能力； (a) 中间体中离域烯丙基阴离子的分子内羟醛反应，1,2-加合物的 Brook 重排产物，以及 (b) 环丙醇酯的氧阴离子加速乙烯基环丙烷重排，环丙醇酯衍生自 1,2-加合物，通过 Brook 重排/环丙烷化序列。为了获得对这一提议的支持，我们利用丙烯酰基硅烷与烯醇锂到乙酸叔丁酯的反应，比较了苯硫基和三甲基甲硅烷基的α-碳阴离子稳定能力，提供了1,2-加成产物和Brook重排/烯丙基重排乘积的比例反映了b-取代基对α-碳负离子稳定能力的差异。我们研究了低温氧阴离子加速乙烯基环丙烷-环戊烯重排，使用四种异构乙烯基环丙乙酸酯与MeLi（2.2当量）的反应，以取决于乙烯基硅烷几何形状的比例提供环戊烯醇和未环化的烯醇甲硅烷基醚。