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New Factors Governing Stereoselectivity in Borohydride Reductions ofβ‐ D ‐Glycoside‐2‐uloses − The Peculiar Effect of “Activated” DMSO
Author(s) -
Kerékgyártó János,
Rákó János,
Ágoston Károly,
Gyémánt Gyöngyi,
Szurmai Zoltán
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200012)2000:23<3931::aid-ejoc3931>3.0.co;2-w
Subject(s) - stereoselectivity , chemistry , acetal , steric effects , selectivity , disaccharide , stereochemistry , glycoside , medicinal chemistry , organic chemistry , catalysis
Comparative evaluation of the manno / gluco ratios obtained in the conventional reductions of β‐ D ‐glucoside‐2‐uloses ( 1 − 4 , 13 and 14 ) reveals the influence of the substitution pattern: the presence of a 4,6‐ O ‐acetal function results in lower stereoselectivity in the monosaccharide‐uloside cases and low stereoselectivity in the disaccharide‐uloside cases, while the absence of a 4,6‐ O ‐acetal group provides distinctly higher stereoselectivity. The 3‐ O ‐benzyl and 3‐ O ‐allyl ethers vicinal to the carbonyl to be reduced have a similar influence on the steric outcome of the carbonyl reduction. A peculiar effect of acetoxydimethylsulfonium acetate (“activated” DMSO) was observed. In all cases, its presence strongly increased the manno ‐selectivity of the reduction. A simple, preparatively expedient, commonly suitable protocol has been elaborated for achieving high manno ‐selectivities and, hence, satisfactory yields.