[kamiyu]

Hi

Is it possible to use just one equivalent of t-BuLi for lithiation?

I saw a paper which stated using one equivalence of t-BuLi and the yield is reported to be 90%.

Not sure if there is something wrong

[Dan]

I saw a paper which stated using one equivalence of t-BuLi and the yield is reported to be 90%.

The yield of what? What's the reaction?

[kamiyu]

The yield of final product

The reaction is just lithiation, followed by external quench

[orgopete]

If the lithiIation product is isobutane, then only one equivalent is needed. If it is a transmetallation reaction and the product is a t-butyl bromide or iodide, then a second equivalent will convert the t-butyl bromide to isobutylene plus isobutane.

[Dan]

The reaction is just lithiation

Deprotonation or Li-Hal exchange? It makes a difference (see orgopete's post).

[kamiyu]

Thanks for your reply, Dan

It is lithium-bromo exchange, i.e. bromobenzene turned into lithiobenzene, followed by Negishi coupling

[Dan]

I was under the impression that 2 equiv. would be required due to elimination of HBr from t-BuBr, but I have no hands-on experience with t-BuLi. Can you give the reference (journal/year/page, don't upload the copyright pdf)?

[kamiyu]

Thank you Dan

You are exactly right. I think the same that one more equiv is needed becasue the resulting tert-butyl bromide is not stable (dehydrohalogenation) by t-BuLi

Therefore, the following scheme is weird and the paper says it is ~90%.

[orgopete]

Hi

Is it possible to use just one equivalent of t-BuLi for lithiation?

I saw a paper which stated using one equivalence of t-BuLi and the yield is reported to be 90%.

Not sure if there is something wrong

This question and the example shows how difficult it can be for a poster to attempt to answer a general question. We suggested reasons why one or two equivalents might be preferred. However, our generalizations did not take into account the possible reaction rates. If someone asked whether you could acylate an amine in water, if you think of a Schotten-Baumen reaction, this would work, if it were acetyl chloride, probably not.

The Neigishi coupling may very well change the reaction. I'm only looking at the scheme and not the complete experiment. If this were a one pot reaction in which t-butyllithium were slowly added last, if the coupling were faster than deprotonation of the t-butyl bromide by-product, then it could proceed with one equivalent.