title: Regioselective ring opening of exo- and endo-3,4-benzylidene acetals of arabinopyranoside derivatives with Lewis acids and reducing agents.
abstract: Dioxolane type 3,4-benzylidene acetals of benzyl β-l-arabinose either as a mixture or pure exo- and endo-isomers cleavaged with BF(3)·OEt(2)/Et(3)SiH in dichloromethane or acetonitrile regioselectively, provided the 4-O-benzyl-3-hydroxy derivative. The reaction with TiCl(4)/Et(3)SiH or Cu(OTf)(2)/Et(3)SiH provided a mixture of 3- and 4-O-benzyl derivatives whereas with Cu(OTf)(2)/BH(3)·THF gave only hydrolyzed product. The regioselectivity of the reaction was proved to be directed by the acetyl substitution at C-2. Benzyl substitution provided a mixture of 3- and 4-O-benzyl derivatives in 1:1 ratio whereas non-substitution yielded the same mixture in 2:1 ratio.
authors: Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Kasetsart University, Chatuchak, Bangkok 10900, Thailand.
authors: Janjira
authors: J
authors: Rujirawanich
authors: Boonsong
authors: B
authors: Kongkathip
authors: Ngampong
authors: N
authors: Kongkathip
mesh_terms: D000080:Acetals / Q000737:chemistry*; D001089:Arabinose / Q000031:analogs & derivatives / Q000737:chemistry*; D001597:Benzylidene Compounds / Q000737:chemistry*; D007536:Isomerism; D058116:Lewis Acids / Q000737:chemistry; D019163:Reducing Agents / Q000737:chemistry
chemical_list: D000080:Acetals; D001597:Benzylidene Compounds; D058116:Lewis Acids; D019163:Reducing Agents; D001089:Arabinose