[kanonsviel]

What does it give by applying Mg to a ketone? I have searched many places, yet had few clues...
And, what product is gained in a reaction between a Grignard reagent and boric acid?

[jake.n]

For the first reaction, you're looking at a nucleophile (Grignard) and an electrophile (Boric Acid).  Which is more basic, hydroxide or your Grignard reagent?

For the second reaction, Magnesium is an "active metal" (i.e. reducing agent)

[kanonsviel]

So,the product of the first reaction should be PhB(OH)2??
and the second an alcohol?
Do I get it right?

[kingsfan]

correct

[jake.n]

I think the boronic acid is right.

Upon further digging, I'm not sure the magnesium will reduce the ketone to an alcohol without an acidic proton.  This
 
http://books.google.com/books?id=w9lTxIaPCQIC&pg=PA240&lpg=PA240&dq=magnesium+benzene+reduction+of+ketones&source=bl&ots=KwfboIyzW6&sig=5367vUvgra5wI8kHHPi-fTarfVc&hl=en&ei=pyXWTNz2J8qgnge5y83kCQ&sa=X&oi=book_result&ct=result&resnum=10&ved=0CDUQ6AEwCQ#v=onepage&q&f=false

suggests that the reaction yields a dimerized, vicinal diol.

[kanonsviel]

I get it, that's an enough hint, thanks for your help

[karvon]

It shouldn't be that the Grignard reagent just deprotonate the boric acid and RH is produced?

[jake.n]

I don't believe boric acid is a proton donor, it's just electropositive.