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  • Title: Regioselective ring opening of benzylidene acetal protecting group(s) of hexopyranoside derivatives by DIBAL-H.
    Author: Tanaka N, Ogawa I, Yoshigase S, Nokami J.
    Journal: Carbohydr Res; 2008 Oct 13; 343(15):2675-9. PubMed ID: 18718576.
    Abstract:
    The reductive ring-opening reaction of benzylidene-protected glucosides and mannosides such as methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-d-glucoside (1) and methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-d-mannoside (4) by using a toluene stock solution of DIBAL-H and a dichloromethane stock solution of DIBAL-H gives mainly or selectively the corresponding 2,3,4-tri-O-benzyl derivatives (2, 5) and 2,3,6-tri-O-benzyl derivatives (3, 6), respectively, although that of methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-d-galactoside (7) gives methyl 2,3,6-tri-O-benzyl-alpha-d-galactoside (9) selectively irrespective of the solvent of the stock solution of DIBAL-H. Similarly, the reaction of the exo-isomer of methyl 2,3:4,6-di-O-benzylidene-alpha-d-mannopyranosides (exo-10) with a toluene stock solution and dichloromethane stock solutions of DIBAL-H selectively gives methyl 3-O-benzyl-4,6-O-benzylidene-alpha-d-mannoside (12) and methyl 2-O-benzyl-4,6-O-benzylidene-alpha-d-mannoside (11), respectively, although that of endo-10 selectively affords 11, irrespective of the solvent of the stock solution of DIBAL-H.
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