Some observations on the reductive ring opening of 4,6-O-benzylidene acetals of hexopyranosides with the borane trimethylamine–aluminium chloride reagent

Reductive ring openings of 3-O-benzoyl-4,6-O-benzylidene-d-glucopyranosides with BH3·NMe3–AlCl3 are accompanied by side reactions, such as debenzoylation and reduction of the benzoate to benzyl ether. This phenomenon was rationalized by aluminium chelate formation between the O-4 acetal and the benzoyl carbonyl group oxygens. It was also shown that these side reactions can be eliminated by using BH3·THF as the reducing agent.