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Does $\ce{LiAlH4}$ and $\ce{NaBH4}$ reduce an isolated epoxide? I have two books where both are saying differently. One says it can and other says cannot. On searching the web there was no definite answer. Can they reduce epoxide to diol or something else ?

I am aware of the reduction of the other groups in the picture:

question no 31, paper 2, chem

Sources: NCERT: yes; JEE Advanced 2016 paper solution by Arihant: no; multiple coaching stuff: both yes/no

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    $\begingroup$ Is that a 5 bond carbon on the epoxide on the left? $\endgroup$ – user137 Sep 16 '20 at 13:23
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    $\begingroup$ Please correct the molecular diagram of the starting material. $\endgroup$ – Waylander Sep 16 '20 at 13:27
  • $\begingroup$ this is NOT an isolated epoxide $\endgroup$ – Waylander Sep 16 '20 at 13:51
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The correct question (taken from the 2016 JEE Paper is): question no 31, paper 2, chem

Lithium Aluminium Hydride reduces epoxides1, hence (A) would not give the required product. LAH also reduces ethers to primary alcohols, which is an easier way of eliminating the option (A). $\ce{BH3}$ in THF can reduce the acid, as explained in this question, hence the requisite product would not be obtained.

$\ce{NaBH4}$ cannot reduce esters, acids or epoxides in the absence of catalysts such as $\ce{PdCl2}$ or $\ce{AlCl3}$ and diglyme, hence (C) would be a correct option here.

Can you tell what Raney Ni would do here?

Raney Ni Reduces carboxylic acid and esters at elevated temperature (eg: $\pu{350 K}$); and no reaction with epoxide. So, it can be used for selective reduction of aldehyde at room temperature ($\pu{298 K}$).

Use this resource to help yourself out and as a reference for such reactions in the future.

References:

  1. Murphy, David K., et al. “Reduction of Epoxides. III. Lithium Aluminum Hydride and Mixed Hydride Reduction of Some Secondary-Tertiary Epoxides.” Journal of the American Chemical Society, vol. 91, no. 10, May 1969, pp. 2649–53. doi:10.1021/ja01038a042.
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  • $\begingroup$ Oh okay! I wasnt aware of the catalyst thing. Would NaBH4 reduce an isolated epoxide without catalyst PdCl2 ? $\endgroup$ – Shaurya Goyal Sep 16 '20 at 17:50
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    $\begingroup$ No, it would not $\endgroup$ – Waylander Sep 16 '20 at 20:36

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