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GATE 2020 CY – Question 11

Organic Chemistry · Reduction: Catalytic homogeneous and heterogeneous hydrogenation. Metal based reductions using Li/Na in liquid ammonia, magnesium, zinc, titanium, and samarium. Hydride transfer reagents: NaBH4, L-selectride, K-selectride, Luche reduction, LiAlH4 and DIBAL-H. · 1 mark · Multiple choice

Which reagents achieve the shown major-product transformation of cyclopent-2-enone into the corresponding allylic alcohol?

Diagram for GATE 2020 CY question 11
  1. $H_2,\ Pd/C$
  2. $H_2N{-}NH_2,\ KOH,\ \Delta$
  3. $NaBH_4/CeCl_3\cdot7H_2O$
  4. $Li/\text{liquid }NH_3$

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Correct answer: (C) $NaBH_4/CeCl_3\cdot7H_2O$

Explanation

The transformation reduces the carbonyl to an alcohol while preserving the conjugated C=C bond. Luche conditions, $NaBH_4/CeCl_3$, favour 1,2 reduction of the enone and give the allylic alcohol, C. Catalytic hydrogenation tends to reduce the alkene, Wolff–Kishner removes the carbonyl oxygen, and dissolving-metal reduction does not provide the selected chemoselective alcohol conversion.

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