November 13, 2024, 02:07:05 AM
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Topic: Need some helped with reaction with ketone to form silyl enol ethers  (Read 2359 times)

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Offline poonilization

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I have a question on a worksheet that i'm not too sure how to answer.

The questions are:

Identify reagents and conditions for the regioselective formation of silyl enol ethers G and H from ketone F.

Enolates are ambident nucleophiles. In the context of the formation of silyl enol ethers G and H from ketone F, explain the term "ambident" and hence rationalise the formation of the silyl enol ether product in these cases.

Picture of reaction attached.

Offline clarkstill

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Re: Need some helped with reaction with ketone to form silyl enol ethers
« Reply #1 on: November 06, 2014, 06:26:17 AM »
You need to show some working. What do you know about kinetic vs. thermodynamic enolization?

Offline poonilization

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Re: Need some helped with reaction with ketone to form silyl enol ethers
« Reply #2 on: November 06, 2014, 06:36:54 AM »
Kinetic enolates form on the less hindered carbon using a bulky base whereas a thermodynamic enolate forms at the more hindered position using a less hindered base but requires greater temperature and reaction times.

So G is the thermodynamic product and H is the kinetic product

Offline poonilization

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Re: Need some helped with reaction with ketone to form silyl enol ethers
« Reply #3 on: November 10, 2014, 07:09:25 PM »
So using TMSCl with a base such as Et3N forms the thermodynamic product (G).

However i am unsure how to for the kinetic silyl enol ether, if i were to use LDA and form the kinetic product with O-Li+ group, could i then react that with TMSCl to form OTMS?

Offline clarkstill

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Re: Need some helped with reaction with ketone to form silyl enol ethers
« Reply #4 on: November 13, 2014, 06:44:07 AM »
Yeah that'll work. It's a hard electrophile so it goes for oxygen.

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