1. T. Eicher and S.Hauptmann , The Chemistry of Heterocycles , Wiley-VCH , Weinheim , 2nd edn, 2003 , p. 94
2. J. Elguero , in Pyrazoles: Comprehensive Heterocyclic Chemistry II , Elsevier , Oxford , 1996 , vol. 3 , p. 1 and references cited therein
3. J. Marchand-Brynaert and L.Ghosez , in Recent Progress in the Chemical Synthesis of Antibiotics , ed. G. Lukacs and M. Ohno , Springer , Berlin , 1990