Reductive openings of benzylidene acetals. Kinetic studies of borane and alane activation by Lewis acids.
The reaction kinetics for a number of reductive openings of methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-D-glucopyranoside have been investigated. Openings to give free HO-6 (using BH(3) x THF-AlCl(3)-THF or LiAlH(4)-AlCl(3)-Et(2)O) follow first order kinetics, while reactions yielding free HO-4 (using BH(3) x NMe(3)-AlCl(3)-THF or BH(3) x NMe(3)-BF(3) x OEt(2)-THF) follow higher order kinetics. The addition of water to the BH(3) x NMe(3)-AlCl(3)-THF results in faster reactions. The BH(3) x SMe(2)-AlCl(3)-THF system constitutes a borderline case, yielding both free HO-6 (by a first order reaction) and free HO-4 (by a higher order reaction). These results correlate well with the concept of regioselectivity by activation of borane complexes.
Johnsson
Richard
R
Organic Chemistry, Lund University, PO Box 124, SE-221 00 Lund, Sweden.
Cukalevski
Risto
R
Dragén
Fanny
F
Ivanisevic
Damir
D
Johansson
Ida
I
Petersson
Linn
L
Wettergren
Erika Elgstrand
EE
Yam
Ka Bo
KB
Yang
Beatrice
B
Ellervik
Ulf
U
D000080:Acetals / Q000737:chemistry*; D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000737:chemistry; D001597:Benzylidene Compounds / Q000737:chemistry*; D001880:Boranes / Q000737:chemistry*; D002236:Carbohydrate Conformation; D002712:Chlorides / Q000737:chemistry; D007700:Kinetics; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry; D010084:Oxidation-Reduction
D000080:Acetals; D017607:Aluminum Compounds; D001597:Benzylidene Compounds; D001880:Boranes; D002712:Chlorides; D009844:Oligosaccharides; D000077410:Aluminum Chloride