Question

How do you form `"ROMgI"` from `"RMgI"` reacting with ketones?

Answer 1

Oh, you're referring to a Grignard Reagent variant. Normally you should see `-O-MgBr` more often. I saw this in second-semester Organic Chemistry.

http://chemwiki.ucdavis.edu/?title=Organic_Chemistry/Aldehydes_and_Ketones/Synthesis_of_Aldehydes_%26_Ketones/Grignard_Reagents

While the formation of `R-O-Mg-I` from `R-Mg-I` needs to be dry `-MgBr` in the presence of water, the hydrolysis process of `R-O-Mg-I` is actually acid-catalyzed. Also, what's attached to the `-Mg-I` must be alkyl or aryl (R = alkane or 1-benzene derivative), at least for `R-Mg-Br`.

Normally, a carbonyl group is a good electrophilic site because basically, it has a high electron density, and it has two p orbitals within its pi bond that have unoccupied space (antibonding atomic orbitals) for electrons in the pi bond to move into (unshaded).

Magnesium, on the other hand, is a strong Lewis acid, so it's a strong electron acceptor. As a result, `-MgI` becomes a great electrophilic site, since nucleophiles are electron donors.