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

Abstract

Carbene insertion into the C(sp2)−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 α‐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.

Borane-Catalyzed Coupling of Diazooxindoles and Difluoroenoxysilanes to Tetrasubstituted Monofluoroalkenes

“…In particular, B­(C 6 F 5 ) 3 has been proven to activate diazo reagents to generate carbene intermediates due to their high Lewis acidity and the vacant p orbital in the boron center . Various B­(C 6 F 5 ) 3 -catalyzed reactions via diazo activation, − including C–H, O–H, N–H, and S–H insertion, C–C bond formation, and annulation reactions have been developed recently. However, CC bond-forming reactions utilizing diazo compounds as a carbene synthon under borane catalysis are still under development.…”