α-oxo-acetals (3b, 5b, 17, 18) through an enolization/ionization mechanism. With trifluoroethanol/sodium trifluoroethoxide, the corresponding trifluoroethyl acetals (3a and 5a) are formed. Basic hydrolysis affords 2-endo-hydroxynorbornene-2-exo-carboxylic acid (20x) and the 7-oxa analogues (22x, 23x), presumably through benzilicacidrearrangement of the α-diketones.