Amino Acids in Heterocyclic Synthesis: Novel Synthesis of Pyrano[2,3‐c]pyrazoles, Pyrazolo[3,4‐b]pyridine, and Pyrido[1,2‐a]benzimidazoles

Abstract

The diazolones 1a–c were reacted with triethylorthoformate and hippuric acid derivatives 3 to afford the novel pyrano[2,3‐c]pyrazole derivatives 4. The latter undergoes ring cleavage by reaction with acetic acid‐ammonium acetate and was transformed into the corresponding pyrazolo[3,4‐b]pyridine derivatives 6. The reaction of 2‐cyanomethyl‐benzimidazole 7 with triethylorthoformate and hippuric acid derivatives 3 to give the pyrido[1,2‐a]‐benzimidazoles 10 has also been discussed.