Use of Polymers as Protecting Groups in Organic Synthesis. Application of Polystyrylboronic Acid to the One-Pot Synthesis of Acylated Carbohydrate Derivatives

The reactions of polystyrylboronic acid with various glycosides show that the polymer is an efficient and very selective protecting group for cis diols. Coupling of the glycosides to the polymer yields the most stable five-or six-membered ring boronate. Examples of diol protection in the formation of selectively acylated glycosides via one-pot reactions include the protection of 2,3-diols in methyl α-L-rhamnopyranoside and methyl α-D-mannopyranoside; 2,4-diols in methyl D-xylopyranosides, methyl β-D-ribopyranoside, and methyl α-D-glucopyranoside; 4,6-diols in methyl α-D-galactopyranoside and methyl α-D-glucopyranoside. In addition, the polymer can be used to protect one of the two 4,6-diol groupings of a disaccharide such as α,α-trehalose. The main advantages of the polymeric protecting group are its selectivity, its insolubility which allows all the reactions to be carried out rapidly and in one pot, and the extreme mildness of the conditions which are required for its use. In addition, the polymer is reusable without regeneration and no loss of activity is observed with repeated use.