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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:

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  • $\begingroup$ @Nilay Ghosh NCERT - yes, jee advanced 2016 paper solution by arihant - no , multiple coaching stuff - both yes/no $\endgroup$ – Shaurya Goyal Sep 16 at 13:05
  • $\begingroup$ Include this information into the question body. $\endgroup$ – Nilay Ghosh Sep 16 at 13:14
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    $\begingroup$ Is that a 5 bond carbon on the epoxide on the left? $\endgroup$ – user137 Sep 16 at 13:23
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    $\begingroup$ Please correct the molecular diagram of the starting material. $\endgroup$ – Waylander Sep 16 at 13:27
  • $\begingroup$ this is NOT an isolated epoxide $\endgroup$ – Waylander Sep 16 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? Use this resource to help you 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 at 17:50
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    $\begingroup$ No, it would not $\endgroup$ – Waylander Sep 16 at 20:36

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