132
2
General Synthetic Methods
⊡ Scheme 30
Examples of stannyl mediated regioselective benzoylation
⊡ Scheme 31
Reagent-dependent multiprotection of methyl β-D-galactopyranoside
tion of O-acyl derivatives is a much faster reaction in any solvent, and it does not require
heating or the presence of an additional nucleophile. Thus, treating methyl α-D-glucopyranoside with (Bu 3 Sn) 2 O and then with BzCl gave the 2,6-di-O-benzoate, while the 3,6-di-Obenzoates were obtained upon analogous benzoylation of methyl β-D-galactopyranoside and
methyl α-D-mannopyranoside, respectively ( > Scheme 30) [230].
An extension of this tin chemistry to the regioselective acylation of unprotected sugars bound
to a resin shows the possibility of using solid-phase techniques for the preparation of O-acyl
derivatives of carbohydrates [231]. Very recently, it has been reported that organotin-mediated
multiple carbohydrate esterifications can be controlled by the acylating reagent and the solvent
polarity. When acetyl chloride is used, the reactions are under thermodynamic control, whereas
when acetic anhydride is employed, kinetic control takes place ( > Scheme 31) [232].
2
General Synthetic Methods
⊡ Scheme 30
Examples of stannyl mediated regioselective benzoylation
⊡ Scheme 31
Reagent-dependent multiprotection of methyl β-D-galactopyranoside
tion of O-acyl derivatives is a much faster reaction in any solvent, and it does not require
heating or the presence of an additional nucleophile. Thus, treating methyl α-D-glucopyranoside with (Bu 3 Sn) 2 O and then with BzCl gave the 2,6-di-O-benzoate, while the 3,6-di-Obenzoates were obtained upon analogous benzoylation of methyl β-D-galactopyranoside and
methyl α-D-mannopyranoside, respectively ( > Scheme 30) [230].
An extension of this tin chemistry to the regioselective acylation of unprotected sugars bound
to a resin shows the possibility of using solid-phase techniques for the preparation of O-acyl
derivatives of carbohydrates [231]. Very recently, it has been reported that organotin-mediated
multiple carbohydrate esterifications can be controlled by the acylating reagent and the solvent
polarity. When acetyl chloride is used, the reactions are under thermodynamic control, whereas
when acetic anhydride is employed, kinetic control takes place ( > Scheme 31) [232].