Studies towards the synthesis of Fipronil® analogues: improved decarboxylation of α-hydrazonoacid derivatives

The Mannich reaction of hydrazones coupled with a [4+1] cycloaddition with isocyanides has been used for the synthesis of aminopyrazole analogues of Fipronil®. The starting cyanohydrazone was prepared with new experimental conditions for efficient diazonium coupling in fluorinated solvents followed by a new sodium cyanide catalysed decarboxylation.