Chemical Research Center, Hungarian Academy of Sciences, H-1025 Budapest, Hungary.
J Org Chem. 2011 Nov 18;76(22):9362-9. doi: 10.1021/jo201645t. Epub 2011 Oct 27.
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.
6-甲基取代的 2-芳基和 2-苄基噻吩并[2,3-b]吡啶鎓 N-酰亚胺与过量的异氰酸酯反应，生成 N,N-二取代的非环 1H-咪唑并[4,5-b]吡啶-2(3H)-酮。这些产物很容易自发地发生[1,5]氢迁移，生成杂芳基咪唑并吡啶酮异构体。这种转化意味着[1,2,4]三唑并[2,3-a]吡啶鎓盐的初始形成，随后是亚甲基部分的去质子化和氨基甲酰化，最后是[1,3]σ迁移重排。反应机理表明，环转化步骤是一个非协同的两步反应机制，一些实验结果也证实了这一点。
