Write a reasonable mechanisms for the following reaction

Hello all! I'm stuck on this one question and am not sure how to finish the mechanism. What I did was attack the alkyne first with the N farthest to the left. I'm not sure what do to after that though. Any help would be greatly appreciated! Thank you!

  • 1
    $\begingroup$ Michael attack by the ring N, as you describe then cyclisation onto the protonated CN by the exocyclic NH2 $\endgroup$
    – Waylander
    Jun 6, 2018 at 16:05
  • $\begingroup$ I’m trying to figure out how or what to attack after the ring-nitrogen attack of the alkyne. When I attack the resulting product from the first step with the exocyclic N I get a very strained cyclic structure with two consecutive alkenes within the 6 membered heterocycle. Does that sound like the right way to do this mechanism? $\endgroup$ Jun 6, 2018 at 16:50
  • $\begingroup$ That doesn't sound right. The neutral intermediate has an acrylonitrile unit added to the ring N, and =NH exo to the ring. $\endgroup$
    – Waylander
    Jun 6, 2018 at 17:43
  • $\begingroup$ I think I got it... 1) attack alkyne with cyclic N and protonate nitrile 2) push LP on nitrile-N back into conj. system and protonate one of the alkenes, getting the the acrylonitrile intermediate you mentioned 3) attack nitrile-C, forming a six membered ring 4) delocalize middle N LP to the left most N $\endgroup$ Jun 6, 2018 at 19:22
  • $\begingroup$ Don't forget the contribution of the ring O to step 3 $\endgroup$
    – Waylander
    Jun 7, 2018 at 7:40


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