[beacon]

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I'm trying to figure out the mechanism of this reaction, so far with no success. I've searched for any clue in "Handbook of Grignard Reagents" and "Grignard Reagents: New Developments", I've also used the reaxys database. I would be grateful for any advice how to approach this problem. Thank you in advance.

[orgopete]

I suspect there is an error in the problem.

[Kadabrium]

oops thereare many losses of hydrogen..

[orgopete]

I don't see where the oxygen is coming from. If there was a dione intermediate, I would have expected the other phthalide to form.

[beacon]

I suspect there is an error in the problem.

That's what I thought in the first place, but there's a little chance for that. It's the reaction scheme I got from professor on my seminar classes.
Another information I got is the yield of this product - 86%.

Hydrogen losses? That's just a scheme of this reaction. Part of the problem is to figure out the possible co-products.

[Dan]

I think it should be CHCCH₂MgBr... after HCl treatment that will give the product in the scheme [chem. commun. 1996, 19-20]. The exact reaction in the original post is not known in the literature (Scifinder/Reaxys). sec-Porpylmagnesium bromide would have to react in a very unusual fashion in order to give the desired product - including undergoing a 4 electron oxidation in the absence of an (obvious) oxidising agent. I think there's a mistake - but if this reaction works I'd love to know why!

[Honclbrif]

I think it should be CHCCH₂MgBr... after HCl treatment that will give the product in the scheme [chem. commun. 1996, 19-20]. The exact reaction in the original post is not known in the literature (Scifinder/Reaxys). sec-Porpylmagnesium bromide would have to react in a very unusual fashion in order to give the desired product - including undergoing a 4 electron oxidation in the absence of an (obvious) oxidising agent. I think there's a mistake - but if this reaction works I'd love to know why!

Likewise, I can't see any good way that this reaction could proceed as written. However, I have been surprised before.