Abstract Hexafluoroacetone (HFA) reacted regiospecifically with various enol silyl ethers at− 30 to− 35 C in the presence of a Lewis acid to give HFA aldols, or α-bis (trifluoromethyl) hydroxymethyl carbonyl compounds, in good yields. The reaction of HFA with dienol silyl ethers, on the other hand, cleanly proceeded even in the absence of a Lewis acid to provide [4+ 2] cycloadducts, or bistrifluoromethylated tetrahydropyran-4-one derivatives, ...
