Ru(ii)-catalyzed regioselective [4 + 1] redox-neutral spirocyclization of aryl amidines with diazopyrazolones: direct access to spiro[indole-3,4′-pyrazol]-5′-ones

An efficient protocol to construct spiro[indole-3,4′-pyrazol]-5′-ones via ruthenium( ii )-catalyzed selective C–H bond activation/[4 + 1] spirocyclization starting from easily available N -aryl amidines and diazopyrazolones has been developed.