Answer:
React it with CH₃MgBr and work up the product with saturated ammonium chloride solution
Explanation:
Grignard reagents convert esters into tertiary alcohols.
The general equation is
The Grignard reagent in this synthesis is methylmagnesium bromide. You prepare it by reacting a solution methyl bromide in anhydrous ether with magnesium and a few crystals of iodine.
The reaction consumes 3 mol of CH₃MgBr per mole of dimethyl carbonate, and everything happens in the same pot.
Acid workup of the product usually involves the addition of a saturated aqueous solution of ammonium chloride and extraction with a low-boiling organic solvent.
The mechanism involves:
Step 1. Nucleophilic attack and loss of leaving group
(a) The Grignard reagent attacks the carbonyl of dimethyl carbonate, followed by (b) the loss of a methoxide leaving group.
Step 2. Nucleophilic attack and loss of leaving group
(a) A second mole of the Grignard reagent attacks the carbonyl of methyl acetate, followed by (b) the loss of a methoxide leaving group.
Step 3. Nucleophilic attack and protonation of the adduct.
(a) A third mole of the Grignard reagent attacks the carbonyl of acetone, followed by (b) protonation of the alkoxide to form 2-methylpropan-2-ol.
