Synthesis of Indazolones via Friedel-Crafts Cyclization of Blocked (Masked) N-Isocyanates.

Nitrogen-substituted isocyanates (N-isocyanates) are rare amphoteric reagents with high, but underdeveloped synthetic potential. Herein, we study the formation of indazolones by Friedel-Crafts cyclization of N-isocyanates using blocked (masked) N-isocyanate precursors: the effect of the masking group and the reaction scope have been delineated. Substrate synthesis has also been improved using a reported copper-catalyzed coupling of arylbismuth(V) reagents that is compatible with the hemilabile OPh blocking group.