The reductive cleavage of 4,6-O-arylmethylene acetals of hexopyranosides is an effective method for the regioselective formation of a benzyl-type ether at either the C-4 or the C-6 hydroxyl group. The compatibility of this method with Ley's butane diacetal (BDA) protection was studied. 4,6-O-(2-Naphthyl)methylene, benzylidene, and p-methoxybenzylidene acetals were introduced to 2,3-O-BDA-protected gluco- and galactosides, and the bis-acetalated products were subjected to reductive acetal openings with different reagents. LiAlH4-AlCl3 reduced the 4,6-acetals with complete chemo- and regioselectivity to give the corresponding 4-O-ethers. The use of Et3SiH-BF3·Et2O led to a mixture of differently reduced products, because transformation of the 4,6-acetal into the related 6-O-ether and reduction of the BDA system into a butane-2,3-diyl group took place competitively. BH3·NMe3-AlCl3 selectively cleaved the 4,6-acetal ring to give the 6-O-ethers as the major or exclusive products.
- Protecting groups
- Ring opening
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry