アミン媒介の電離性アレンボリレーションのメカニズム研究と,MIDAボロナート合成におけるその応用
Viktor Bagutski1, Alessandro Del Grosso, Josue Ayuso Carrillo
1Department of Chemistry, University of Manchester, Manchester, M13 9PL, United Kingdom.
Journal of the American Chemical Society
|December 5, 2012
まとめ
アレンとヘテロアレンの直接の電離性ボリレーションは,Y(2) BClとAlCl(3) をアミンで使って達成される. この方法は,安定したMIDA-ボロナートを生成し,活性化基質のためのボレニウムカチオンを持つS(E) Arメカニズムを経由して進行します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 有機金属化学 有機金属化学
- 合成方法論 合成方法論
背景:
- 電子性ボリレーションは,オルガノボロン化合物を合成するための重要な変換です.
- 直接ボリレーションのための効率的で汎用的な方法の開発は,依然として活発な研究分野です.
研究 の 目的:
- 多種多様なアレンとヘテロアレンに対して,直接の電離性ボリレーション法を開発する.
- 反応機構を調査し,重要な中間物質を特定する.
- 安定したMIDA-ボロナートの合成を可能にします.
主な方法:
- Y(2)BCl (Y(2) = Cl(2) またはo-catecholato) を用いて,等分アルCl(3) と三次アミンを用いた直接の電離性ボリレーション.
- ArBCl (((2) の TMS (((2) MIDA を使った製品のインシット機能化.
- 反応メカニズムを解明するために,実験と計算の研究を組み合わせた.
主要な成果:
- 多種多様なアレンとヘテロアレンを,中等から良好な収穫量でボリレーションに成功する.
- ベンチ安定のMIDA-ボロナートの形成.
- ボレニウムカチオン, [Y(2) B(アミン) ](+) を,活性化アレンのS(E) Arメカニズムにおける主要な電友として識別.
- カテチョラトボロケーションの2つのアミン依存経路の解明.
- 低活性化アーレンの代替メカニズムと,ボリュックなアミンとの反応が特定されました.
結論:
- 多用途の直接電離性ボリレーションプロトコルが確立されています.
- この研究は,様々な芳香質基質のボリル化に関する機械的洞察を提供します.
- 開発された方法は,価値あるMIDA-ボロナート構成要素への実用的な経路を提供します.
関連する概念動画
Hydroboration-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.
Preparation of Amines: Reductive Amination of Aldehydes and Ketones
Carbonyl compounds and primary amines undergo reductive amination first to produce imines, followed by secondary amines in the same reaction mixture, using selective reducing agents like sodium cyanoborohydride or sodium triacetoxyborohydride. Reductive amination produces different degrees of substitution of amines depending on the starting amine substrate.
Alkynes 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.
Regioselectivity 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.
Amines to Amides: Acylation of Amines
Various carboxylic acid derivatives (such as acid chlorides, esters, and anhydrides) can be used for the acylation of amines to yield amides. The reaction requires two equivalents of amines. The first amine molecule functions as a nucleophile and attacks the carbonyl carbon to produce a tetrahedral intermediate. This is followed by the loss of the leaving group and restoration of the C=O bond.
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary amide...
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary amide...
Electrophilic Aromatic Substitution: Nitration of Benzene
The nitration of benzene is an example of an electrophilic aromatic substitution reaction. It involves the formation of a very powerful electrophile, the nitronium ion, which is linear in shape. The reaction occurs through the interaction of two strong acids, sulfuric and nitric acid.


