Improved synthesis of 2,3:4,6-di-O-isopropylidene-d-glucopyranose and -d-galactopyranose

2,3:4,6-Di-O-isopropylidene-d-glucopyranose and -d-galactopyranose acetals are conveniently prepared by hydrogenolysis of benzyl 2,3:4,6-di-O-isopropylidene-β-d-glucopyranose and -β-d-galactopyranose in almost quantitative yields in 3 h. This result is in contrast with the sluggish reaction observed (48 h) when the hydrogenolysis was carried out on either anomeric α,β mixtures or on the corresponding α anomers.