Cobalt‐Catalyzed Switchable [4 + 1] and [4 + 1 + 1] Spirocyclization of Aromatic Amides with 2‐Diazo‐1H‐indene‐1,3(2H)‐dione: Access to Spiro Indene‐2,1'‐isoindolinones and Spiro Isochroman‐3,1'‐isoindolinones

Comprehensive Summary Herein, we report a condition‐controlled divergent synthesis of spiro indene‐2,1'‐isoindolinones and spiro isochroman‐3,1'‐isoindolinones through cobalt‐catalyzed formal [4 + 1] and [4 + 1 + 1] spirocyclization of aromatic amides with 2‐diazo‐1 H ‐indene‐1,3(2 H )‐ dione. When the reaction is carried out under air in ethyl acetate, spiro indene‐2,1'‐isoindolinones are formed through Co(II)‐catalyzed C—H/N—H [4 + 1] spirocyclization. When the reaction is run under O 2 in CH 3 CN, on the other hand, spiro isochroman‐3,1'‐isoindolinones are generated through Baeyer‐Villiger oxidation of the in situ formed spiro indene‐2,1'‐isoindolinones with O 2 as a cheaper and environmental‐friendly oxygen source. In general, these protocols have advantages such as using non‐precious and earth‐abundant metal catalyst, no extra additive, high efficiency and regioselectivity. A gram‐scale synthesis and the removal of the directing group further highlight its utility.