Borane‐Catalyzed, HFIP‐Assisted Carbene Insertion into Internal Alkenyl C−H Bonds under Metal‐Free Conditions

Carbene insertion into the C(sp(2))-H bonds of internal alkenes was enabled in air by HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) as both the mediator and solvent through its cooperation with borane B(C6F5)(3) as the catalyst. 3-Diazooxindoles and 3-diazoindolin-2-imines were amenable to work as the carbene precursors, and alpha-oxo ketene dithioacetals acted as the internal alkenes at ambient temperature. The present synthetic protocol features metal-free conditions, diverse substituent tolerance, and 47-84% yields, offering an efficient route to 3-vinylated oxindole and indole derivatives.