Pentafluorophenylammonium Trifluoromethanesulfonimide: Mild, Powerful, and Robust Catalyst for Mukaiyama Aldol and Mannich Reactions between Ketene Silyl Acetals and Ketones or Oxime Ethers

Abstract Pentafluorophenylammonium trifluoromethanesulfonimide (C 6 F 5 N + H 3 ⋅NTf 2 − ) promotes Mukaiyama aldol and Mannich reactions using ketene silyl acetals with ketones and oxime ethers, respectively. The present robust method is mild, but powerful enough to utilize less accessible electrophiles such as enolizable ketones and oxime ethers to produce a variety of β‐hydroxy esters and β‐alkoxyamino esters, respectively. Mechanistic investigation revealed in situ generation of trimethylsilyl bistriflimide Tf 2 N(TMS), the truly active catalyst, which was supported by rational 1 H NMR measurements.