Question

The correct option(s) of reagents and reaction sequences suitable for carrying out the following transformation is/are: 

• A. (i) NBS, (PhCOO)₂;   (ii) aq. NaOH;   (iii) active MnO₂;   (iv) Li/liq. NH₃, t-BuOH
• B. (i) m-CPBA;  (ii) BF₃·Et₂O
• C. (i) SeO₂;   (ii) Dess–Martin periodinane;   (iii) K[BH(s-Bu)₃] (K-selectride)
• D. (i) dil. KMnO₄;   (ii) NaIO₄

Hint:

Sequential allylic functionalization (via bromination or oxidation) followed by mild selective oxidation and 1,4-reduction is an effective strategy for converting alkenes to ketones.

Answer 1

The Correct Option is A, C

The transformation is the conversion of cyclohexene to cyclohexanone. We must identify sequences that achieve this selectively.

• (A)
  • (i) NBS, (PhCOO)₂ → Allylic bromination of the double bond.
  • (ii) aq. NaOH → Nucleophilic substitution to form allylic alcohol.
  • (iii) MnO₂ → Selective oxidation of allylic alcohol to enone.
  • (iv) Li/NH₃, t-BuOH → Birch reduction: 1,4-reduction of enone to ketone.
  • This sequence is well-known for such transformations. CORRECT
• (B)
  • (i) m-CPBA → Epoxidation of alkene.
  • (ii) BF₃·Et₂O → Lewis acid mediated ring opening.
  • This sequence does not lead efficiently to ketone. WRONG
• (C)
  • (i) SeO₂ → Allylic oxidation.
  • (ii) Dess–Martin periodinane → Oxidation to enone.
  • (iii) K-selectride → 1,4-reduction to ketone.
  • This route is synthetically reliable. CORRECT
• (D)
  • (i) dil. KMnO₄ → Oxidative cleavage may occur.
  • (ii) NaIO₄ → Cleaves vicinal diols or enediols.
  • These do not lead selectively to cyclohexanone. WRONG

\[ \boxed{\text{Correct options: (A), (C)}} \]