Synthesis of spiro-3H-indazoles via 1,3-dipolar cycloaddition of arynes with 6-diazocyclohex-2-en-1-one derivatives and fused-2H-indazoles by subsequent rearrangement

A route to rare spiro-3H-indazoles bearing a carbonyl group adjacent to the spirocyclic quarternary carbon via 1,3-dipolar cycloaddition reaction of arynes with 6-diazocyclohex-2-en-1-one derivatives under mild conditions has been developed. Further transformation of these unique spiro-3H-indazoles via an acid- or heat-mediated rearrangement to fused-2H-indazoles and an interesting reduction/ring-opening/reduction sequence are also described.