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
Asymmetric synthesis of optically pure α-methyl-β,γ-unsaturated ketones via triethylaluminum-mediated stereospecific pinacol rearrangement of alkenyl groups
Optically pure α-methyl-β,γ-unsaturated ketones are synthesized by the Et3Al-mediated pinacol-type rearrangement where alkenyl groupsmigrate stereospecifically with complete retention of the olefin-geometry.