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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:

enter image description here

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

enter image description here

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

Can someone please explain why this happened?

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  • $\begingroup$ Can you work on getting that reference? I am getting feedback on my answer asking for it, but you made the claim. Thanks! $\endgroup$
    – Oscar Lanzi
    Commented May 18, 2018 at 12:30
  • $\begingroup$ @OscarLanzi Sorry... but at my current level its impossible to procure citations. All claims made here are according to what my instructor taught me... $\endgroup$
    – Soham
    Commented May 18, 2018 at 17:23

1 Answer 1

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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.

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    $\begingroup$ Do you have a reference for that? $\endgroup$
    – Waylander
    Commented May 18, 2018 at 10:58
  • $\begingroup$ 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. $\endgroup$
    – Oscar Lanzi
    Commented May 18, 2018 at 11:10
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    $\begingroup$ @OscarLanzi Can you explain formation of 'carbanion'? $\endgroup$
    – Soham
    Commented May 18, 2018 at 18:13

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