P. Barili, G. Catelani, F. Colonna
Jun 15, 1988
Citations
0
Influential Citations
14
Citations
Journal
Carbohydrate Research
Abstract
Abstract Kinetically controlled reaction of 4.5 equiv. of 2-methoxypropene with some alkyl α- and β- d -galactopyranosides gave the 2,3:4,6-di- O -isopropylidene derivatives in high yields (80–85%). With 2 equiv. of 2-methoxypropene, benzyl β- d -galactopyranoside gave the 4,6- and the 3,4-monoacetals in the ratio 30:1 together with ∼20% of the 2,3:4,6-diacetal. The structures of methyl 2,3:4,6-di- O -isopropylidene-α- and -β- d -galactopyranosides were determined by X-ray analysis. The former crystallised in the orthorhombic system, P 2 1 2 1 2 1 , with a = 5.503, b = 16.105, c = 16.822 A, and Z = 4, the latter in the monoclinic system, P 2 1 , with a = 10.400, b = 13.344, c = 11.647 A, β = 111.50, and Z = 4. The α anomer and the two molecules of the β anomer had the d -galactopyranoside and the 1,3-dioxane rings in twist-chair conformations and the dioxolane ring in a half-chair conformation. N.m.r. spectroscopy suggested the occurrence of similar conformations in solution.