定向金属 (oxo) 亚利法性C-H氧化:主要的基质偏差
Marinus A Bigi1, Sean A Reed, M Christina White
1Department of Chemistry, Roger Adams Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
Journal of the American Chemical Society
|May 22, 2012
概括
一个新的指导策略利用碳酸团来指导金属催化C-H基化. 这种方法克服了固有的偏见,使得像paclitaxel这样的复杂分子能够精确氧化.
科学领域:
- 有机金属化学 有机金属化学
- 有机合成 有机合成
- 催化剂是一种催化剂.
背景情况:
- C-H 基化是有机合成中至关重要的转化.
- 非血红素铁复合物提供了有前途的催化活性,但由于电子和硬质因素而面临选择性挑战.
- 通常需要指导小组来实现特定站点的功能化.
研究的目的:
- 描述金属 (oxo) 促进的C-H基化中的指导作用的第一个一般策略.
- 为了证明碳素酸部分如何克服铁催化C-H氧化中的不利偏差.
- 为了在复杂的自然产品框架中实现特定地点的氧化.
主要方法:
- 使用非黑米铁复合物Fe (PDP) 作为催化剂.
- 作为指导部分,使用的基板含有碳素酸功能组.
- 研究了帕克利塔塞尔框架的C-H氧化,以证明其指导作用.
主要成果:
- 碳氧酸组成功指导了C-H化,克服了电子,固态和立体电子偏差.
- 定向效应使氧化从帕克利塔塞尔中受益的C-1通路转移.
- 在帕克利塔塞尔中实现了C-2氧化与自然氧化状态和立体配置的安装.
结论:
- 已经建立了使用碳酸酸的金属 (oxo) 促进的C-H氧化定向的一般策略.
- 这种方法提供了一个强大的工具,用于控制挑战性C-H功能化反应的位点选择性.
- 这种方法可以合成复杂的分子,以选择性氧化帕克利塔塞尔为例.
相关概念视频
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
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.
01:25Radical Anti-Markovnikov Addition to Alkenes: Overview
The addition of hydrogen bromide to alkenes in the presence of hydroperoxides or peroxides proceeds via an anti-Markovnikov pathway and yields alkyl bromides.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.