I am stuck at a step in reduction of alkene using $\ce{B2H6}.$ I assume that step 1 is the addition of borane to alkene. After that a water molecule attacks $\ce{-BH2},$ it being a Lewis acid. Subsequently, the boron will depart and oxygen will remove a proton which gets attached to carbanion formed when boron exited.

This is what I think is happening, the sole reason to ask it here is because I am unable to find a mechanism online or from a book. Mostly, I stumble upon hydroboration which is of no use to me. Please correct my mechanism or guide me to a reliable source.

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    $\begingroup$ When you don't find good results, it often means that the search keywords are not appropriate. Use Google Scholar in such cases. I typed "mechanism of alkene reduction by diborane" in Google Scholar, and the second result is a >20 paged review. I don't have an answer but you can certainly start from there. Anything which is in a textbook is often 20-30 years old research. Here is the link to the review: pubs.acs.org/doi/abs/10.1021/cr60304a005 $\endgroup$
    – AChem
    Aug 23, 2019 at 20:39
  • $\begingroup$ What are you talking about? You want to make triple bond diborane? With what base? This is at least weird... $\endgroup$
    – Mithoron
    Aug 23, 2019 at 21:16
  • $\begingroup$ @Mithoron I was talking about reduction by diborane $\endgroup$ Aug 24, 2019 at 1:55
  • $\begingroup$ Aditya, I am not an organic chemist so I don't know the answer. My point was that the answer must be out there if you use the right keywords. Search this phrase "mechanism of hydroboration of alkenes". I see several papers right away some of them can be downloaded. It is definitely complex because I see lot of papers on this topic. Are you in a university of college? $\endgroup$
    – AChem
    Aug 24, 2019 at 2:04
  • $\begingroup$ I'm still in school , last year $\endgroup$ Aug 24, 2019 at 2:08

1 Answer 1


Addition of boron hydrides to alkenes or alkyne is a valuable reaction in organic chemistry. The reaction is called hydroboration that gives organoboron compounds, which are a valuable group of intermediates for other organic synthesis (Chem.libretexts.org). The simplest borane, $\ce{BH3}$, exists as the dimer, $\ce{B2H6}$, or in complexed form with certain ethers (e.g., $\ce{H3B}$-THF) or sulfides (e.g., $\ce{H3B-S(CH3)2}$). To my understanding, your expectation is to find a mechanism for hydroboration of an alkene by borane followed by its oxidation to corresponding alcohol. I found a suitable mechanism for that online and depicted in following diagram. First step is common hydroboration.


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    $\begingroup$ No I was looking for a mechanism that converts alkene to alkane , instead of oxidation as the second step if an acid is used instead in aqueous medium then the mechanism follows the process I described in my question, fortunately I could find it in the link given by you itself , so thank you. $\endgroup$ Aug 24, 2019 at 3:43

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