ABSTRACT
Experimental ............................................................................................................ 11 General Methods ................................................................................................. 11 General Procedures ............................................................................................. 11 Phenyl 2,3,4-tri-O-benzyl-1-thio-β-d-glucopyranoside (5) ................................ 12 Methyl 2,3-di-O-benzyl-4-O-diphenylmethyl-α-d-glucopyranoside (6) ............ 13 Phenyl 2,3-di-O-benzyl-4-O-(2-naphthyl)methyl-1-thio-β-dglucopyranoside (7) ............................................................................................. 13 Phenyl 2,3-di-O-benzyl-4-O-(4-methoxybenzyl)-1-thio-β-dglucopyranoside (8) ............................................................................................. 13
Acknowledgments .................................................................................................... 14 References ................................................................................................................ 18
Regioselective reductive openings of the 4,6-O-benzylidene-type acetals of hexopyranosides to the corresponding benzyl-type ethers are important methods in carbohydrate chemistry. The transformation requires a hydride donor reagent in combination with a protic or a Lewis acid. Depending on the applied reagents and conditions, either the 4-OH or the 6-OH groups can be liberated. In the rst synthetically applicable method, which was elaborated by Lipták et al.,1 4,6-O-benzylidene acetals of hexopyranosides were reacted with LiAlH4 and AlCl3 to give 4-O-benzyl ethers with a free 6-OH group. The NaCNBH3-HCl reagent system introduced by Garegg et al.2 resulted in opposite regioselectivity and thus became complementary to the LiAlH4-AlCl3 method. After publication of these two classical procedures, various reagents have been introduced for regioselective cleavage of 4,6-O-benzylidene-type acetals.3-22 However, the regioselectivities and yields of the reactions are often inuenced by the structure of the substrate and neighboring substituents. The LiAlH4-AlCl3 reagent in combination with CH2Cl2-Et2O as solvent is often reliable in providing the 4-O-alkyl derivatives in high yield and regioselectivity. The limitation of this process is the incompatibility of ester, amide, and imide substituents with these reaction conditions.
