在4--1-氧基循环化中的6-endo选择性上
Jens Hartung1, Rainer Kneuer, Christian Rummey
1Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. hartung@chemie.uni-kl.de
Journal of the American Chemical Society
|September 24, 2004
概括
研究了替代剂对激素循环的作用. 增加替代剂批量增强了6-内分泌触发的选择性,由于有利的FMO相互作用和减少扭曲应变,有利于四胺基的形成.
科学领域:
- 有机化学 有机化学
- 计算化学计算化学
- 反应机制 反应机制
背景情况:
- 激素循环是有机合成中的关键反应.
- 了解区域选择性对于控制反应结果至关重要.
- 替代效应可以显著影响反应通路.
研究的目的:
- 为了研究4-置换的4--1-氧基循环的区域选择性.
- 阐明了不同的环形大小 (四二与四二) 形成的因素.
- 为了将实验观测与计算预测相关联.
主要方法:
- 结合实验调查和使用密度函数理论 (DFT) 的计算研究.
- 替代剂的系统变化在乙烯基的4-位置.
- 过渡状态能量和几何参数的分析.
主要成果:
- 随着替代剂大小的增加 (H < CH3 < C(CH3) 3 < C6H5),观察到6内触发选择性的逐渐增加.
- 对于较小的替代剂而言,四氨酸 (5-exo-trig) 的形成更受青.
- 对于 tert-butyl 和 phenyl 替代剂而言,首选的是 tetrahydropyran 形成 (6-endo-trig).
结论:
- 区域选择性是由扭曲应变和边界分子轨道 (FMO) 相互作用之间的平衡所支配的.
- 通过降低过渡状态能量,FMO相互作用有利于大容量替代物的6内分触发循环.
- 扭曲应变在6内触发路径中起作用,但在5外触发路径中没有作用.
相关概念视频
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
03:00Preparation of Epoxides
Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
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01:26Photochemical Electrocyclic Reactions: Stereochemistry
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Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
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