The presence of water improves reductive openings of benzylidene acetals with trimethylaminoborane and aluminium chloride.
The acidic reagent formed in situ from anhydrous AlCl(3) and H(2)O in 3:1 ratio is much more efficient for the reductive openings of the cyclic benzylidene acetals with Me(3)N x BH(3) in tetrahydrofurane than the AlCl(3) alone. Under proposed conditions, the dioxane-type 4,6-O-bezylidene acetals of hexopyranosides give regioselectively the corresponding 4-hydroxy,6-O-benzyl derivatives in excellent yields. Reductive openings of the dioxolane-type 3,4-O-benzylidene acetals of galactopyranoside are also very efficient and regioselective and give either 3-O-benzyl derivative (from 3,4-O-exo-benzylidene acetal) or 4-O-benzyl derivative (from 3,4-O-endo-benzylidene acetal) depending on the configuration of the acetal carbon atom.
Sherman
Andrei A
AA
N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky prospect 47, Moscow 119991, Russia.
Mironov
Yuri V
YV
Yudina
Olga N
ON
Nifantiev
Nikolay E
NE
D000080:Acetals / Q000737:chemistry*; D017607:Aluminum Compounds / Q000737:chemistry*; D001597:Benzylidene Compounds / Q000737:chemistry*; D001880:Boranes / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D006601:Hexoses / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry*
D000080:Acetals; D017607:Aluminum Compounds; D001597:Benzylidene Compounds; D001880:Boranes; D002712:Chlorides; D006601:Hexoses; D014867:Water