Pyrazolo[3,4-b]pyridines have been obtained by the condensation of 5-amino-4-cyanopyrazole, readily available by the reaction of dithioacetals with substituted hydrazines, with β-ketoesters or β-diketone in the presence of tin(IV) chloride at reflux temperature in dry toluene.
(a) KuoS.C., HuangL. J., and NakamuraH., J. Med. Chem., 1984, 27, 539; (b) R. Motokuni, M. Tauaka, S. Hashimoto, and T. Suzue, JP 77 78,895 (1977); Chem. Abstr., 1977, 87, 168 629; (c) U. Schindler, K. Schoenafinger, and H. Strobel, DE 19,744,027 (1999); Chem. Abstr., 1999, 130, 267435; (d) J. E. Macor and G. Yu, WO 2000 015 222 (2000); Chem. Abstr., 2000, 132, 237 088; (e) A. Straub, A. Feurer, C. Fuerstner-Robyr, C. Alonso-Alija, J.-P. Stasch, E. Perzborn, J. Huetter, K. Dembowsky, and E. Stahl, DE 19 834 045 (2000); Chem. Abstr., 2000, 132, 137 398.
2.
(a) SabithaG., SrividyaR., ArchanaB., and YadavJ. S.Synth. Comm., 1999, 29, 655; (b) V. K. Ahluwalia and B. Goyal, Synth. Comm., 1996, 26, 1341; (c) J. Quiroga, B. Insuasty, S. Cruz, P. Hernandez, A. Bolaños, and R. Moreno, J. Heterocyclic Chem., 1998, 35, 333; (d) F. M. Abd El Latif; M. A. Barsy, E. A. Elrady, and M. Hassan, J. Chem. Res., (S), 1999, 696; (e) V. K. Ahluwalia and A. Dahiya, Indian J. Chem., 1996, 35B, 1208.
3.
(a) VeroneseA.C., CallegariR., BasatoM., and ValleG., J. Chem. Soc., Perkin Trans. 1, 1994, 1779; (b) A. C. Veronese, V. Gandolfi, M. Basato, and B. Corain, J. Chem. Res. (S), 1988, 246.
4.
(a) VeroneseA.C., CallegariR., and MorelliC. F., Tetrahedron, 1995, 51, 12277; (b) A. C. Veronese, R. Callegari, and S. A. A. Salah, Tetrahedron Lett., 1990, 31, 3485.
5.
TominagaY., HonkawaY., HaraM., and HosomiA., J. Heterocyclic Chem., 1990, 27, 775.
6.
(a) JunjappaH., IlaH., and AsokanC. V., Tetrahedron, 1990, 46, 5423; (b) R. K. Dieter, Tetrahedron, 1986, 42, 3029
