A Facile Synthesis of Pyrido[2^′,3^′:3,4]pyrazolo[1,5-a]pyrimidine and Pyrido[2^′,3^′:3,4]pyrazolo[5,1-c][1,2,4]triazine Bearing a Thiophene Moiety

Scheme 3

Synthesis of pyrido[2′,3′:3,4]pyrazolo[5,1-c][1,2,4]triazines 21a,b and 24a–c.