Controlled formation of dipyranoside derivatives through C6 and O4. Pyranosidic homologation. VII

Abstract

. Can. J. Chem. 65,2834Chem. 65, (1987. A procedure has been developed for pyranosidic homologation of methyl a-D-glucopyranoside via C4 and C6. Reaction of the aldehydo group of compound 2 with the Wittig-Bestmann reagent, Ph3P=CHCH(OEt)2, gave an E / Z mixture of acetals, 4, which cyclizes under the specific catalysis of pyridinium p-toluenesulfonate and in the presence of alcohols to give anomerically pure olefinic bipyranosides, 6a-d. A general procedure for epoxidation of the latter involves osmium tetroxide hydroxylation, followed by reaction with phosgene iminiumchloride (Viehe's salt) to give chlorocarbamates 12 and 13, which are then subjected to the action of sodium methoxide. This allows for the formation of a single series of diastereomeric epoxides, 7, and controlled cleavage of the latter with nucleophiles then follows well-established precedents. Selective access to the "ends" of the bipyranosides 7c and d can be obtained by oxidative removal of the activated benzyl glycosides with DDQ.BRUCE FRANCIS MOLINO et BERT FRASER-REID. Can. J. Chem. 65,2834Chem. 65, (1987 (7); un clivage selectif de ces demiers a I'aide de nuclCophiles se produit en suivant les precedents bien Ctablis. On peut acceder d'une fa~on stlective aux aboutsn des bipyrannosides 7c et 7d en proctdant un enltvement oxydatif des glycosides de benzyle actives par du DDQ.[Traduit par la revue]In an effort to extend the range of simple sugar derivatives to accommodate increased numbers of contiguous chiral centers, we have developed a process termed pyranosidic homologation in which a "satellite" pyranose ring is appended to a "primary" ring (1). The assembly obtained thereby provides additional stereogenic centers, which can be manipulated according to well-precedented transformations from the carbohydrate literature. This principle is illustrated in Chart l for the bipyranose I, whose substituents, X and Y, can be introduced into I1 by taking advantage of the highly developed chemistry of unsaturated sugars (2, 3). The efficient formation of bipyranose I1 from a monopyranose precursor, 111, is an obvious first step. In this manuscript, we give details of our studies related to the transformations I11 -+ I1 -+

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

“…Thus beginning with a D-glucopyranoside 3, retrosynthesis led to tripyranoside 2 which could accommodate eight of the nine contiguous chiral centers of 1. Tripyranoside 2 was indeed prepared [12], and a number of transformations afforded the bipyranoside 4 [13,14].…”