LANTHANIDE TRIFLATES AS WATER-TOLERANT LEWIS-ACIDS - ACTIVATION OF COMMERCIAL FORMALDEHYDE SOLUTION AND USE IN THE ALDOL REACTION OF SILYL ENOL ETHERS WITH ALDEHYDES IN AQUEOUS-MEDIA

Lanthanide trifluoromethanesulfonates (triflates), especially ytterbium triflate (Yb(OTf)(3)), were found to be stable Lewis acids in water. In the presence of a catalytic amount of lanthanide triflate, formaldehyde in water solution (commercial formaldehyde solution) was activated and the hydroxymethylation reaction of silyl enol ethers proceeded smoothly. Lanthanide triflates were also quite effective in the aldol reaction of silyl enol ethers with aldehydes in aqueous media, and water-soluble aldehydes such as acetaldehyde, acrolein, and chloroacetaldehyde could be employed for direct use. Moreover, in all these reactions, lanthanide triflates were quantitatively recovered after the reactions were completed and could be reused.