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 ytterbiu m triflate (Yb(OTf)(3)), were found to be stable Lewis acids in water. In the presence of a catalytic amount of lanthanide triflate, formald ehyde in water solution (commercial formaldehyde solution) was activat ed 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 wat er-soluble aldehydes such as acetaldehyde, acrolein, and chloroacetald ehyde could be employed for direct use. Moreover, in all these reactio ns, lanthanide triflates were quantitatively recovered after the react ions were completed and could be reused.