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As there is no ring expansion I'm assuming that a carbocation should not form at ester carbon as it leads to ring expansion. But is there any an exception to it? Also the hint provided along with this question says "use ethylene glycol". How does ethylene glycol help here?

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    $\begingroup$ Actually you just have to reduce the ether. The reason you use ethylene glycol is to block the carbonyl by forming an acetal as the ketone can get reduced too. $\endgroup$
    – Sameer Thakur
    Jun 23, 2019 at 17:35
  • $\begingroup$ okay we can now use lialh4 followed by h+ addition to yield alcohol but how does the acetal revert back to ketone? $\endgroup$
    – raj pattnaik
    Jun 23, 2019 at 17:50
  • $\begingroup$ Just hydrolyze it again. $\endgroup$
    – Sameer Thakur
    Jun 23, 2019 at 17:51
  • $\begingroup$ @SameerThakur Sorry, my page was not updated when I looked at it. Never mind. $\endgroup$
    – Karsten Theis
    Jun 26, 2019 at 20:10

2 Answers 2

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Example 1

Ethylene glycol is often used to make cyclic acetals; its acetals are called ethylene acetals (or ethylene ketals).This interconversion makes acetals attractive as protecting groups to prevent ketones and aldehydes from reacting with strong bases and nucleophiles

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Example 2

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Reference

Page 861, Organic Chemistry , Eight edition , L.G.Wade

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The hint is to form the dioxolane (cyclic acetal) of the ketone with ethylene glycol then reduce the ester (LiAlH4 will do this, the dioxolane will not react) and finally deprotect the ketone. The reduction can also be accomplished by hydrolysing the ester and reducing the resulting acid with borane.

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