Selective acylation of 6-deoxyglycals

L-Rhamnal was acylated under a variety of conditions with various acylating reagents. Substitution of the hydroxyl group in the allylic position was favored when acetyl chloride, N-acetylimidazole, benzoyl chloride, and N-benzoylimidazole were used (40-60% net yields), whereas the homoallylic group of L-rhamnal was selectively protected when acetic anhydride-pyridine was employed for the acylation. The monoacetates of L-fucal underwent O-3----O-4 migration of the acetyl group, and selective acylation of this glycal could not be achieved.