Reaction of 5-t-butyl-2-methoxy-3H-azepine (2) with nuclephiles (alkoxides or t-butyllithium) gave respective substitution product at 2-position of the ring. Unexpectedly, when methyllithium was used as a nucleophile, bis(5-t-butyl-3H-azepin-2-yl)methane (7), the structure of which found to be tautomeric vinamidine (7a,b), was formed. Tautomerization between 7 and 7a,b was characterized spectroscopically and theoretically based on the levels of B3LYP/631G(d).