The Rearrangement of Acetylated and Benzoylated β-Glucosides Catalyzed by Titanium Tetrachloride²

Abstract

Titanium tetrachloride catalyzes the formation of an equilibrium mixture of benzoylated noil-aromatic glucósidos in which the -isomer greatly predominates over the /3-isomer. The reaction provides a convenient method of preparing the -glucosides from their anomers.The transformation of the benzoylated /3-glucosides occurs more readily than that of the corresponding acetates. Application of the isorotation rules has indicated that when benzoates are compared with their corresponding acetates benzoylation is found to have increased the dextrorotation of the Cz-C8 portion of glucoside molecules and to have decreased the influence of the aglucone upon the rotation. Six new, crystalline glucoside derivatives and a crystalline compound containing o-nitrophenol, titanium and chlorine in the ratio 2:1:2 have been prepared.

The SYNTHESIS OF 3-O-[(Benzylthio)carbonyl]-Β-D-Glucopyranose AND METHYL 2,4,6-Tri-O-Benzoyl-Α AND Β-D-Glucopyranosides

“…Peracetylated hexoses are converted to the acetochlorohexose on treatnlent with titanium tetrachloride in chloroform (9). This method has been shown, more recently, to be applicable to perbenzoylated glucose derivatives (8,10). The presence of the (benzy1thio)carbonyl group did not cause any anonlalous behavior during the use of this reagent.…”

SnCl4- and TiCl4-Catalyzed Anomerization of Acylated O- and S-Glycosides: Analysis of Factors That Lead to Higher α:β Anomer Ratios and Reaction Rates

“…The equilibrium α:β ratio also depended on the nature of the protecting group, being consistently higher when benzoate protecting groups were used as opposed to acetyl protecting groups (cf. entries 2 vs 3, 4 vs 5, 1 vs 7, 9 vs 10, and 13 vs 14) . The rate was faster for the tetra- O -methyl-protected derivative 8 when compared with 7 by a factor of ∼20 although the stereoselectivity for anomerization of 8 was not as high as that for 7 …”

Selective electrochemical glycosylation by reactivity tuning1

“…The reaction mixture was diluted with dichloromethane (200 ml), washed with water (100 ml), brine (150 ml), dried (MgSO 4 ) and concentrated in vacuo to afford phenyl glycoside 13 (8.4 g, 89%) as a white crystalline solid, m.p. 169-171 °C (ethyl acetate/petrol) (lit., 23 172-174 °C); [] 24 D +81 (c, 1.0 in CHCl 3 ) {lit., 23 [] 20 D +84.0 (c, 1.0 in CHCl 3 )};  H (400 MHz, CDCl 3 ) 4.51 (1H, dd, J 5,6 6.1 Hz, J 6,6′ 12.4 Hz, H-6), 4.59 (1H, dd, J 5,6′ 2.6 Hz, H-6′), 4.65 (1H, ddd, J 4,5 10.2 Hz, H-5), 5.54 (1H, dd, J 1,2 3.7 Hz, J 2,3 10.2 Hz, H-2), 5.80 (1H, at, J 9.9 Hz, H-4), 6.05 (1H, d, H-1), 6.46 (1H, at, J 9.8 Hz, H-3), 6.86-7.60 (18H, m, ArH), 7.93-8.04 (7H, m, ArH).…”