Question

The correct sequence of reagents for the following conversion will be :

• A. \(\mathrm{CH_3MgBr,\ H^+/\,CH_3OH,\ [Ag(NH_3)_2]^+OH^-}\)
• B. \(\mathrm{[Ag(NH_3)_2]^+OH^-,\ CH_3MgBr,\ H^+/\,CH_3OH}\)
• C. \(\mathrm{[Ag(NH_3)_2]^+OH^-,\ H^+/\,CH_3OH,\ CH_3MgBr}\)
• D. \(\mathrm{CH_3MgBr,\ [Ag(NH_3)_2]^+OH^-,\ H^+/\,CH_3OH}\)

Hint:

The CHO group must become an ester first (so that it can add two \(\mathrm{CH_3}\) groups to give \(\mathrm{C(OH)(CH_3)_2}\)) while the ketone is left for the Grignard step.

Answer 1

The Correct Option is C

Starting material: 4-formylcyclohexanone (a ketone and an aldehyde). Product: 1,4-disubstituted cyclohexane with \(\mathrm{C(OH)CH_3}\) at the old ketone carbon and \(\mathrm{C(OH)(CH_3)_2}\) at the old aldehyde carbon.
A tertiary \(\mathrm{-C(OH)(CH_3)_2}\) group is obtained from an ester \(\mathrm{-COOCH_3}\) with excess \(\mathrm{CH_3MgBr}\), while the ketone gives \(\mathrm{C(OH)CH_3}\) with one \(\mathrm{CH_3MgBr}\).
Step 1: Tollens' reagent \(\mathrm{[Ag(NH_3)_2]^+OH^-}\) oxidises only the CHO to COOH (the ketone is unaffected).
Step 2: \(\mathrm{H^+/CH_3OH}\) esterifies COOH to \(\mathrm{COOCH_3}\).
Step 3: excess \(\mathrm{CH_3MgBr}\) converts the ketone to \(\mathrm{C(OH)CH_3}\) and the ester to \(\mathrm{C(OH)(CH_3)_2}\).
The Grignard reagent must come last, because it would otherwise be destroyed by the acid or react with the free CHO.
Answer: (3) \(\mathrm{[Ag(NH_3)_2]^+OH^-,\ H^+/CH_3OH,\ CH_3MgBr}\)