Reactions of Grignard Reagent: 1,2 vs 1,4 addition

Question

So I was reading through Grignard reagent and I came across this answer by jerepierre, which mentions:

In general, Grignard reagents and organolithium reagents add directly to the carbonyl carbon, while organocuprates (organocopper reagents) add to the beta-position of an unsaturated ketone.

Now, I want to know, what is the meaning of 'in general'? Can anyone please provide me some cases where the general rules are not followed.

Also, I came to know that:

give 1,4 addition with $\ce{PhMgBr}$ to give:

(that reference is difficult to provide at the moment).

Can someone please explain why this happened?

Can you work on getting that reference? I am getting feedback on my answer asking for it, but you made the claim. Thanks! — Oscar Lanzi, May 18 '18 at 12:30
@OscarLanzi Sorry... but at my current level its impossible to procure citations. All claims made here are according to what my instructor taught me... — Soham, May 18 '18 at 17:23

score 4 · Accepted Answer · answered May 18 '18 at 09:40

4

This is not a 1,4 addition. It is a 1,2 addition across a carbon-carbon double bond. This mode of reaction is unusual for Grignard reagents, but here a highly stabilized "double benzylic" anion is formed and the competitive reaction of adding to the carbonyl group is sterically hindered.

answered May 18 '18 at 09:40

Oscar Lanzi

56,895
4
89
175

1

Do you have a reference for that? – Waylander May 18 '18 at 10:58
I'm going by what the asker posted. The 1,2 attack forming the carbanion is the only way to get the claimed product. I think the asker needs a reference for the claim. – Oscar Lanzi May 18 '18 at 11:10
1

@OscarLanzi Can you explain formation of 'carbanion'? – Soham May 18 '18 at 18:13

Reactions of Grignard Reagent: 1,2 vs 1,4 addition

1 Answers1