ACID-CATALYZED CONVERSION OF 2-O-(2-HYDROXYPROPYL)-D-GLUCOSE DERIVATIVES INTO 1,2-O-(1-METHYL-1,2-ETHANEDIYL)-D-GLUCOSE ACETALS. STUDIES RELATED TO O-(2-HYDROXYPROPYL)CELLULOSE

Article abstract of DOI:10.1016/0008-6215(84)85162-9

The acid-catalyzed solvolysis of methyl 3,5,6-tri-O-benzyl-2-O-(2-hydroxypropyl)-α-D-glucofuranoside (1) in chloroform involves a neighboring-group attack on C-1 by the hydroxypropyl substituent, and opening of the furanoside ring to yield a diastereomeric pair of 3,5,6-tri-O-benzyl-1-Omethyl-1,2-O-(1-methyl-ethanediyl)-D-glucose acetals (2 and 3).The latter, which differ in configuration at C-8,represent a resolution of the enantiomeric forms of the original 2-O-(2-hydroxypropyl) group.In a succeeding reaction, the 1-methoxyl group of each acetal undergoes an intramolecular displacement by O-4, leading to the formation of the corresponding biycyclic acetals, i.e., the two diastereomers (4 and 5) of 3,5,6-tri-O-benzyl-1,2-O-(1-methyl-1,2-ethanediyl)-α-D-glucofuranose.Solvolysis of 6, the β anomer of 1, proceeds in an analogous manner, although more rapidly, to yield a corresponding pair of acyclic-aldose acetals (7 and 8), as well as bicyclic acetals 4 and 5.Similar results are observed for solvolysis in the 2-O-(2-hydroxyethyl) series, whereas the reaction of the 2-O-(2,3-epoxypropyl) counterpart of 1 (or 6) with hydrogen chloride affords the corresponding chloromethyl analogs of 4 and 5.In all of these series, one of each diastereomeric pair of products is more stable than the other, and reasons for this are considered.Evidence based on n.m.r.-spectral data and steric factors is presented to show that the configuration of the chiral center C-8 of 2, 4, and 7 is (S), whereas it is (R) in 3, 5, and 8.Also, conformational characteristics of the various solvolysis products are assessed, and mechanisms possibly involved in their formation are discussed.