Can Organometallics Be Used as Bases in Carbonyl Reactions?

[Upupumiau]

Homework Statement

It's a synthesis, dedicated more to carbonyl reactions. However, there is this step where you deduce the structure of an elongated terminal alkyne and then they tell you to add 1. MeMgBr 2. Formaldehyde.

Homework Equations

Usually organometallics are used to transform the carbonyl group into an alcohol, or to open epoxides. I have been checking books and I could not find a reaction between the alkyne triple bond and organometallics.

The Attempt at a Solution

I suppose that since I can't use them to interact with the triple bond, they have to be used as a base. Am I in the right?

 

[TeethWhitener]

I’m assuming by “organometallic” here you mean the Grignard reagent (MeMgBr). Grignards essentially act as alkyl anion synthons, meaning that you can treat MeMgBr as Me^- for the purposes of this synthesis. And yes, they are extremely basic, which is why they are incompatible with water and alcohols (e.g., pK_a of CH₄ is somewhere around 50, so the conjugate base CH₃^- is about as basic as a compound can be).

The same general considerations apply to analogous alkyllithium, alkylzinc, and alkylmercury compounds (among others).

 

[Upupumiau]

Thank you, it really helped.