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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o1247

The keto aldehyde shown is treated with one equivalent of ethane-1,2-diol and an acid catalyst (water removed), then with sodium borohydride, and finally with dilute aqueous acid. Select the correct statement(s).

  1. AThe aldehyde group is converted into the cyclic acetal in preference to the ketone
  2. BSodium borohydride then reduces the remaining ketone to a secondary alcohol
  3. CThe final aqueous acid step removes the cyclic acetal and releases the aldehyde (free or as its cyclic hemiacetal)
  4. DThe aldehyde carbon ends up as a primary alcohol in the final product

Answer: A, B, C

The aldehyde is more electrophilic and less hindered than the methyl ketone, so with one equivalent of diol it is selectively converted into the dioxolane (4-oxopentanal reacts at C-1). Sodium borohydride then reduces only the free ketone. Dilute acid removes the acetal and releases the aldehyde (which may close to a cyclic hemiacetal). The final product retains the aldehyde carbon in oxidation level, so the claim that both carbonyl carbons end up as alcohol carbons is wrong.
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