Hydroamination Route to Pyridines and Pyrazines

Significance

Reported here is the synthesis of pyridines by intramolecular acid-catalyzed hydro­amination-isomerization-aromatization of alkynyl oximes 1. Whereas the reaction produces N-oxide derivatives by thermolysis, the use of excess of TFA (5 equiv) at high temperature and, even better, catalytic TsOH (2 mol%) afforded pyridines in moderate to very good yields. The reaction was extended to N-Boc alkynyl oximes 2 under the same conditions, which underwent in situ Boc deprotection to afford pyrazines in modest yields.