EXTERNAL AND INTERNAL NUCLEOPHILES AGAINST THE PRIMARY POSITION OF GALACTOPYRANOSIDE DERIVATIVES

In the case of galactopyranoside derivatives benzyloxy and methoxy gro ups situated at position-3 can act as internal nucleophiles against th e primary position, thus forming 3,6-anhydro compounds, and can compet e with external nucleophiles. The competition of external and internal nucleophiles was studied during nucleophilic substitution reactions o f 6-O-tosylated galactopyranoside derivatives, having 3-O-benzyl or 3- O-methyl groups, with sodium azide. The ratio of the obtained intramol ecularly cyclized and externally substituted products was governed by conformational, steric, electronic and anomeric effects, beside the fe ature of the external and internal nucleophiles.