Convenient syntheses of 2,3,4,6-tetra-O-alkylated D-glucose and D-galactose

Convenient syntheses of the 2,3,4,6-tetra-O-benzylated and -allylated D-glucopyranoses 1 and 2 and the corresponding D-galactopyranoses 3 and 4 are described. The D-glucose derivatives 1 and 2 were obtained from inexpensive sucrose by peralkylation and subsequent acid hydrolysis. In this reaction sequence an alkylated D-fructofuranosyl cation is generated which was trapped by different nucleophiles to afford 4-benzyloxymethylenefurfural (8) and the alkylated D-fructosides 7, 8 and 10. On the other hand 2,3,4,6-tetra-O-benzyl-D-galactose 3 was synthesized by oxidative cleavage of ethyl 2,3,4,6-tetra-O-benzyl-1-thio-alpha,beta-D-galactopyranoside (11) with aqueous N-bromosuccinimide. The alternative route for the preparation of 2,3,4,6-tetra-O-allyl-D-glucopyranoside (2) via p-methoxybenzyl beta-D-glucoside is less attractive. However, this route was used for the synthesis of 2,3,4,6-tetra-O-allyl-D-galactose (4).