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I saw a question here about the mechanism for a heterocyclic ring formation: What is a reasonable mechanism for the following reaction?. I tried solving the mechanism but I am missing something. Let me explain my reasoning:

This is the reaction: enter image description here

I started protonating the nitrile N, followed by the attack of the cyclic N to the terminal alkyne carbon. Then I couldn't figure out what happens next, so I assumed the triple bond attacks a proton and forms the acrylonitrile intermediate (I am 99.99% sure this is not what happens). Then the exo N attacks the nitrile carbon and form the 6-membered ring, followed by a proton exchange between the imino nitrogen and the protonated cyclic amino group (again, I feel this is ridiculously wrong). The lone pair on the cyclic amino group form the double C=N bond, however, I still end with a protonated N that is not in the product.

enter image description here

Can someone explain to me what I am missing?

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – jonsca Jun 20 '18 at 22:38

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