Dioxane-type (2-naphthyl)methylene acetals of glycosides and their hydrogenolytic transformation into 6-O- and 4-O-(2-naphthyl)methyl (NAP) ethers

α-, β-d-Gluco-, galacto-, 2-deoxy-2-phthalimido-β-d-glucopyranosides with different aglycons (methyl, allyl, p-methoxyphenyl, thioethyl) reacted with 2-naphthaldehyde dimethyl acetal to give rise to 4,6-O-(2-naphthyl)methylene acetals. The acetals were converted into fully protected compounds bearing benzoyl, benzyl, allyl, p-methoxybenzyl groups. The fully alkylated dioxane-type acetals were hydrogenolysed with AlH3 (3LiAlH4–AlCl3) reagent to furnish 4-O-NAP/6-OH derivatives. All acetals were treated with BH3·Me3N–AlCl3 in THF and a reverse regioselectivity was observed, producing 6-O-NAP/4-OH derivatives. Similar regioselectivity was also observed by using NaCNBH3–HCl reagent. In all reactions very mild reaction conditions were required, regioselectivity was better than 93:7, and the isolated yields were between 83–92%. All compounds were characterised by 1H and 13C NMR spectra. Solid-state and solution conformation of methyl 2,3-di-O-acetyl-4,6-O-(2-naphthyl)methylene-α-d-galactopyranoside were elucidated by X-ray and NMR measurements.