Name: acyloin condensation: ester coupling pathway
Uploaded: 2023-04-30T11:23:12.000Z
Duration: 1 min 19 s
Channel: JoVE

Pinacol ve McMurry reaksiyonlarının yanı sıra, asiloin yoğunlaşması, esterleri içeren başka bir indirgeyici birleştirme reaksiyonudur.
Bu reaksiyonda, esterler, asiloin olarak da adlandırılan bir α-hidroksi keton oluşturmak için aprotik bir çözücü içinde bir metal elektron kaynağının varlığında reaksiyona girer.
Reaksiyon, kararsız bir tetrahedral ara madde oluşturmak için radikal dimerizasyona uğrayan ve daha sonra daha fazla çökerek 1,2-diketon veren ketillerin oluşumu yoluyla ilerler.
Bir 1,2-diketon, elektrofillere ve indirgeyici maddelere karşı bir ketondan nispeten daha reaktif olduğundan, iki elektronun aktarılması 1,2-diketon'u kolayca bir enediolata indirger.
Son olarak, enediolatın asitleştirilmesi, iyi bir verime sahip bir α-hidroksi keton verir. Bununla birlikte, nükleofilik enediolatın reaktivitesi genellikle yan ürünlerin oluşumuna yol açar.
İstenmeyen yan reaksiyonları önlemek için, enediolatı silillemek için trimetilsilil klorür eklenir ve nihai ürün olarak bir α-hidroksi keton elde etmek üzere sulu asit ile daha da hidrolize edilen bir bis-silil eter verilir.

esterlerin İndirgeyici bağlanması yoluyla α-hidroksi ketonlar: asilloin yoğunlaşmasına genel bakış

&alpha;-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview

Pinacol ve McMurry reaksiyonları ketonların veya aldehitlerin indirgeyici bağlanmasını içerir. Benzer şekilde, iki ester molekülünün aprotik bir çözücü içinde sodyum metali varlığında bimoleküler indirgeyici bağlanması, bir a-hidroksi keton ürününü verir. α-hidroksi ketona asilolin de denir, dolayısıyla reaksiyona 'asilolin yoğunlaşması' adı verilir.

<img alt="Figure1" src="/files/ftp_upload/12908/12908_PT_Figure_1.svg" style="text-align: center; height: 65px;">

Asilolin yoğunlaşma reaksiyonunda esterler, kararsız bir tetrahedral ara ürün oluşturmak üzere radikal dimerizasyona uğrayan ketillere dönüştürülür. Ayrıca bu ara madde çökerek 1,2-diketon ara maddesini verir. 1,2-diketonlar, düşük π* enerjisi nedeniyle elektrofillere ve indirgeyici maddelere karşı ketonlardan nispeten daha reaktiftir. Sonuç olarak, iki elektron sırayla bir endiolat oluşturmak üzere 1,2-diketona aktarılır. Son olarak, enediyolat ara maddesi, iyi bir verime sahip bir a-hidroksi ketonu vermek üzere asit ile söndürülmektedir.

Nükleofilik enediyolatın reaktivitesi nedeniyle çoğunlukla ana ürünün yanında bazı yan ürünler de elde edilir. Yan reaksiyonların üstesinden gelmek ve bir asilolin verimini arttırmak için, endiolatın silillenmesi için trimetilsilil klorür kullanılır. Bu, a-hidroksi ketonları vermek üzere sulu asitle daha da hidrolize edilen bir bis-silil eterle sonuçlanır.

Esterlerin İndirgeyici Bağlanması Yoluyla α-Hidroksi Ketonlar: Asilloin Yoğunlaşmasına Genel Bakış

Pinacol ve McMurry reaksiyonları, ketonların veya aldehitlerin indirgeyici bağlanmasını içerir. Benzer şekilde, iki esterin bimoleküler indirgeyici bağlanması ...

hydroxy-ketones-via-reductive-coupling-esters-acyloin-condensation

Education

JoVE Core

Organic Chemistry

Organik Kimya

Unit 1

Ünite 1

Radical Chemistry

Radikal Kimya

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

acyloin condensation: ester coupling pathway

Acyloin condensation is a reaction that joins two ester molecules to form an alpha-hydroxy ketone. The product is also called an acyloin. In this reaction, sodium metal is used in an aprotic solvent, which supports the reductive coupling step.

The reaction is related to the pinacol and McMurry reactions, which also involve reductive coupling of ketones or aldehydes. Here, the ester first becomes a ketyl. These ketyl species undergo radical dimerization and form an unstable tetrahedral intermediate. That intermediate then collapses to give a 1,2-diketone intermediate.

The 1,2-diketone is more reactive than a ketone toward electrophiles and reducing agents because it has lower pi-star energy. Two electrons then transfer in sequence to form an enediolate. The enediolate is finally quenched with acid to produce the alpha-hydroxy ketone. This reaction can give a good yield, but side products may also form because the enediolate is nucleophilic.

Trimethylsilyl chloride can be used to reduce those side reactions and improve the acyloin yield. It silylates the enediolate to form a bis-silyl ether. Aqueous acid then hydrolyzes this intermediate to give the alpha-hydroxy ketone.

Acyloin Condensation: Ester Coupling Pathway

acyloin-condensation-ester-coupling-pathway

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&alpha;-hydroxy ketones via reductive coupling of esters: acyloin condensation overview

Acyloin condensation is a reaction that joins two ester molecules to form an alpha-hydroxy ketone. The product is also called an acyloin. In this reaction, sodium metal is used in an aprotic solvent, which supports the reductive coupling step. The reaction is related to the pinacol and McMurry reactions, which also involve reductive coupling of ketones or aldehydes. Here, the ester first becomes a ketyl. These ketyl species undergo radical dimerization and form an unstable tetrahedral...

key terms and concepts

Learn how acyloin condensation couples two esters with sodium metal to form alpha-hydroxy ketones, including ketyls, enediolates, and yield improvement.

Acyloin Condensation: Ester Coupling Pathway | JoVE K12

organic chemistry

JoVE Core Organik Kimya, kısa ve anlaşılması kolay animasyonlu video dersleri kullanarak stereokimya, reaksiyonlar ve mekanizmaların temel kavramlarını açıklar. Buna ek olarak, bilim insanlarının yer aldığı videolar, ilgili kavramların günümüz laboratuvarlarında gerçekleştirilen klasik ve orijinal araştırma deneylerinde nasıl uygulandığını göstermektedir.

Acyloin Condensation: Ester Coupling Pathway

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