Grignard reagent + ester → 3° alcohol template

PhMgBr adds to methyl benzoate; the tetrahedral intermediate expels methoxide to give benzophenone, which is more reactive than the ester and takes a second PhMgBr; acid work-up gives triphenylmethanol.

Mechanism step by step

Addition, loss of methoxide to a ketone, then a second addition: two equivalents of R–MgBr

1. First addition – The C–Mg bond attacks the ester C=O
2. Loss of methoxide – C=O re-forms and MeO⁻ leaves: benzophenone
3. Second addition – The ketone reacts faster than the ester: a second PhMgBr adds
4. Acid work-up – The alkoxide is protonated

Key points

• The ketone formed in step 2 is more electrophilic than the ester, so it captures R–MgBr at once: the reaction cannot be stopped at the ketone, and 2 equivalents are needed.
• Two of the three groups on the carbinol carbon come from the Grignard reagent: RCO₂R′ + 2 R″MgBr → RR″₂C–OH. Formate esters give secondary alcohols.
• Strictly dry conditions: water or any O–H/N–H protonates PhMgBr to benzene. Biphenyl (from coupling while the reagent forms) is the usual by-product.
• To stop at the ketone, use a Weinreb amide or a nitrile: their tetrahedral adducts do not collapse until work-up.

Drawn with 193 atoms, 13 arrows, 8 shapes – every one editable in MolDraw.

Sources

• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 10 Textbook
• Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005 Textbook