[poonilization]

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.

[clarkstill]

You need to show some working. What do you know about kinetic vs. thermodynamic enolization?

[poonilization]

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

[poonilization]

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?

[clarkstill]

Yeah that'll work. It's a hard electrophile so it goes for oxygen.