Glucose selective benzoylation

One such example, depicted in Scheme 8.17, incorporates the classical dithioacetal opening of D-glucose. As illustrated, selective benzoylation of the primary hydroxyl, followed by di-acetalization and debenzoylation, afforded alcohol 56. The primary alcohol in 56 was displaced... 

J. M. Williams and A. C. Richardson, Selective acylation of pyranosides I. Benzoylation of methyl a-D-glycopyranosides of mannose, glucose and galactose, Tetrahedron, 23 (1967) 1369-1378. 

In order to selectively modify the 6-hydroxy, the 2, 3-hydroxy, specially the 2-, can be shielded by binding with blocking groups. They reacts with the modification reagent to achieve the modified CDs. For example, first replace all the three hydroxyls of glucose unit using sulfonyl reagent, then remove the 6- substituent by 2- propanol potassium which is mixed in 2-propanol/benzene solution. Thereafter, the relevant modifiers can react with 6- only. Finally, remove the 2, 3- benzoyl via methanol/potassium hydroxide solution. 

Some factors influencing the selectivity of the acetylation of 1,6-anhydro- -D-glucopyranose have been discussed in a theoretical paper. The expected mixture of mono- and di-benzoates was formed when methyl P-D-arabinopyranoside was exposed to 1 or 2 molar equiv. of benzoyl chloride in pyridine at -40 C. The order of reactivity was concluded to be OH-2>OH-4>OH-3 for mono-and OH-2>OH-3>OH-4 for di-benzoylation. For the 2-deoxy-2-amino-a-D-glucose derivative 21,... 

---