The Evans aldol reaction of hexafluoroacetone and trifluoroacetaldehyde causes complete reversal of diastereofacial selectivity. The boron enolate derived from N-acyloxazolidinone 2 reacts with trifluoroacetaldehyde to give anti and “non-Evans” syn aldols with stereoselectivity in the range of 7:3–17:3. With α,α-difluoroaldehyde 4b, a small amount of the normal syn aldol was formed. However, the anti