Trialkylphosphonium Oxoborates as C(sp³)-H Oxyanion Hole and Their Application in Catalytic Chemoselective Acetalization

Trialkylphosphonium oxoborates with site-isolated borate counter anions were found to have preorganized C(sp 3 )–Hs that can interact with electron donors. The system can serve as a mimic of oxyanion holes to catalyze chemoselective acetalization.