Rearrangement of aryl- and benzylthiopyridinium imides with participation of a methyl substituent.
6-Methyl substituted 2-aryl- and 2-benzylthiopyridinium N-imides reacted with an excess of isocyanates to give N,N-disubstituted exocyclic1H-imidazo[4,5-b]pyridin-2(3H)-ones. The products easily underwent spontaneous [1,5] hydrogen shift to provide the heteroaromatic imidazopyridinone isomers. The transformation implied the initial formation of [1,2,4]triazolo[2,3-a]pyridinium salt, followed by deprotonation and carbamoylation of the methylene moiety, and, finally, a rearrangement following a [1,3] sigmatropic pattern. Mechanistic considerations suggest and some experimental findings reveal the nonconcerted two-step mechanism of the ring transformation step.
Chemical Research Center, Hungarian Academy of Sciences, H-1025 Budapest, Hungary.
Roberta
R
Palkó
Orsolya
O
Egyed
Zsuzsanna
Z
Riedl
Tibor András
TA
Rokob
György
G
Hajós