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Katy Caselli

Regioselectivity of the Hydroboration and Epoxidation of Limonene

David Rosen  Follow

Sterics is the deciding factor in hydroboration which occurs at the least hindered carbon, thus you get the primary alcohol from limonene. The hydroboration of limonene is discussed here

MCPBA selectively oxidises the more substituted alkene source here so with limonene the selectivity is the reverse of the hydroboration and the cyclohexene double bond is epoxidised.

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Joseph Waithaka  Follow
chemistry.stackexchange.com/questions/74005/…More
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John Wo  Follow
Thanks for your answer. Is there a reason why sterics is the deciding factor for hydroboration but not for epoxidation? Especially as BH3 (less bulky) is used instead of BHR2 as the reagent.More
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Gerald Cadwell  Follow
That's very helpful, thank you for sharing. I think I understand why epoxidation occurs at the more substituted electron rich bond, however I am still unsure why hydroboration does not follow the same selectivity. Isn't BH3 also acting as an electrophile, so shouldn't it also be attracted to the more electron rich bond? I get why sterics would be the deciding factor if the hydroboration reagent used was bulkier, but in this case it isn't.More
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John Maiko  Follow
@SashaJ Does this answer your question? More
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James Flax  Follow
@SashaJ I cannot immediately answer this. I think it deserves to be a new question.More
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