1. See, for example:
2. Five-membered heteroaromatic rings as intermediates in organic synthesis
3. bHeaney, H.; Ahn, J. S.InComprehensive Heterocyclic Chemistry II;Katritzky, A. R.; Rees, C. W.; Scriven, E. F. V., Eds.; Elsevier:Oxford, 1996; Vol.2, p297.
4. cFriedrichsen, W.InComprehensive Heterocyclic Chemistry II;Katritzky, A. R.; Rees, C. W.; Scriven, E. F. V., Eds.; Elsevier:Oxford, 1996; Vol.2, p.351.
5. dKeay, B. A.; Dibble, P. W.InComprehensive Heterocyclic Chemistry II;Katritzky, A. R.; Rees, C. W.; Scriven, E. F. V.Eds.; Elsevier:Oxford, 1996; Vol.2, p395.