Abstract: The mechanisms of a number of Mukaiyama aldol and Sakurai allylation reactions catalyzed by the Lewis acids [Ti (Cp) 2 (OTf) z], Ph3COTf, and Ph3CC104 have been investigated. It is found that hydrolysis of the Lewis dcid by trace amounts of water in the solvent can lead to the formation of acid. The acid then reacts with the silyl enol ether or allylic silane to generate Me3SiOTf or Me3SiC104, both of which are powerful catalysts for ...