Hi,
I'm trying to explain the formation of the final compound in the reaction of alpha pinene epoxide with ethanol, a very interesting topic in the formation of add-value chemical substances.
I know that the first step is the formation of a bicyclic compound (SN1) that contain both hidroxide and ethoxy like compound in their structure.
But, in the second step is opening the bicyclic structure and I am supposing that ocurrs a [3+3] sigmatropic rearrangement to form the final product.
I am not sure because in the reaction mechanism that I am specullating occur the breaking the internal cyclobutane and after will should occur the formation of the final compound (You can see in the file that I am attaching)
Can you give me an idea about if my idea is correct and if is possible what is the reaction mechanism in the second step?
Thanks a lot.
You have to adhere to two rules in order to write a correct mechanism for this kind of transformation: (1) you need to first protonate your starting material, as all these rearrangements are acid catalyzed, and (2) ethanol addition happens at the last step, "killing" the final cationic intermediate and then transferring the excess proton to the next molecule to start a new rearrangement.
This is a complicated rearrangement and assuming that the starting material and final product structures are correct, I include a 10-step proposed mechanism, by adhering to these two rules. Steps 4 & 5 are the "strangest" but are necessary to produce the final product.
Hope I helped!
Thanasis
Good Morning profesor,
Thank you for your answer.
Best regards,
Julián.
So I have run many acid-catalyzed reactions with alpha-pinene oxide, and the only aldehyde that I've ever observed in any significant quantity is alpha campholenic aldehyde, although I have never done the reaction in ethanol. Could you share your reaction conditions, and your NMR and mass spec data for this compound? Also, you state that you know the first step is addition of the ethoxy group to the epoxide to form an alpha-hydroxy ether- how do you know this? have you isolated this compound? Thank you for your response.- Mitch deLong
Good Morning Professor Mitchell!
Of course, in the case of the reaction of alpha pinene epoxide with acid catalysts the product with a high selectivity is campholenic aldehyde.
But, I am exploring a lot of conditions and with ethanol I was obtained this compound (etanocitronellal) with a high probability (using mass spectrum and the data basis). I didn't isolated this compound because I obtained a lot of compound that in my experimental setup was very complicated to separte using chromatographic column.
Best regards,
Julián.
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