The interaction of fluorosulfonic acid (FsOH) with either bis-trimethylsilyl -acetamide (BTMSA) or -urea (BTMSU) can be used to generate catalytic amounts of trimethylsilylfluorosulfonate (TMSOFs) "in situ" for use in a wide range of reactions as an alternative to trimethylsilyltriflate (TMSOTf): the reduction of acetals by triethylsilane can be achieved using a catalytic amount of FsOH.