2
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Does my suggested mechanism for benzotriazole synthesis look correct? Are the arrows for the cyclization in the right place?

Chemdoodle (which I drew this with) makes the curly arrows look a bit weird.

Proposed mechanism of benzotriazole synthesis

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7
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    $\begingroup$ Too many steps, amino could substitute H2O, then deprotonation. $\endgroup$
    – Mithoron
    Jan 16 at 23:54
  • $\begingroup$ You mean the intermediate with the pendant hydronium would cyclize with expulsion of water? $\endgroup$
    – Jacob
    Jan 16 at 23:55
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    $\begingroup$ Your solution is plausible but I am bothered by the use of structure 7 the way you have. Its too far to reach! If you do an electrocyclization of 7 to form the benzene ring and a 4-membered ring bearing vicinal nitrogens, then you can have the remaining nitrogen as a neutral "nitrene" ready for 1,2-shift of nitrogen and ring expansion. OTOH, acid-catalyzed cyclization of structure 2 followed by dehydration gets you there. $\endgroup$
    – user55119
    Jan 16 at 23:58
  • $\begingroup$ When I was drawing it I figured the electrocyclization through the electronegative N wouldn't work but ended up drawing it anyway. So I was right to be concerned. $\endgroup$
    – Jacob
    Jan 16 at 23:59
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    $\begingroup$ Jacob, you are free to like what you like. I'm not convinced. I'll post an answer. $\endgroup$
    – user55119
    Jan 17 at 0:45

1 Answer 1

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Species 1 is your seventh structure. The C=N=N atoms are linear and a long reach for the remaining nitrogen. Electrocyclization of 1 to 2 restores aromaticity. Nitrene species 3 allows for a 1,2-shift to an electron-deficient center with concommitant loss of strain in the 4-membered ring to produce 1H-benzo[d][1,2,3]triazole 4.

Cyclization of 5 $\rightarrow$ 6 and dehydration via 7 gets the job done. Perhaps @Mithoron knows something that I am not aware of.

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