アリルアルコールの触媒的エナンチオセレクティブジブロミネーション
Dennis X Hu1, Grant M Shibuya, Noah Z Burns
1Department of Chemistry, Stanford University, Stanford, California 94305, United States.
Journal of the American Chemical Society
|August 20, 2013
まとめ
新しいジブロミネーション反応は,ジブロモマロネートとチタンブロミドを使用しています. タルタリック酸由来ダイオルは,リガンド加速度によるエナチオセレクティブ触媒を可能にし,合成化学を前進させる.
科学分野:
- 有機化学 オーガニック・ケミストリー
- カタリシス カタリシス カタリシス
- 合成方法論 合成方法論
背景:
- ディブロミネーション反応は,様々な有機化合物の合成に不可欠です.
- ディブロミネーションのためのエナチオセレクティブの方法の開発は,有機合成における重要な課題です.
研究 の 目的:
- 容易に入手可能な試薬を用いた新しい二ブロミネーション反応を開発する.
- この二ブロミネーションプロセスでエナチオセレクティブの触媒作用を達成するために.
主な方法:
- ブロモニウム源としてディブロモマロネートを使用した.
- ブロミド源としてチタンブロミド種を使用した.
- エナチオセレクティブ・カタリシスのキラルリガンドとしてタタリック酸由来ダイオルを組み込みました.
主要な成果:
- 新しいジブロミネーション反応を成功裏に開発した.
- ディブロミネーション反応で高いエナチオ選択性を達成した.
- ワイン酸由来ダイオールによるリガンド加速度効果が実証された.
結論:
- 開発された二ブロミネーション反応は,新しい合成経路を提供する.
- エナチオセレクティブ・カタリシスは,タタリック酸由来ダイオルを用いて実現可能である.
- この方法は,非対称合成のための貴重なツールを提供します.
関連する概念動画
01:27Radical Substitution: Allylic Bromination
In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...
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.
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.
02:46Halogenation of Alkenes
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
02:41Formation of Halohydrin from Alkenes
An alkene, such as propene, reacts with bromine in the presence of water to yield a halohydrin. Halohydrins contain a halogen and a hydroxyl group attached to adjacent carbons. When the halogen is bromine, it is called a bromohydrin, while a chlorohydrin has chlorine as the halogen.
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.