Some aspects of the formation of hex-2-enopyranosides from methyl 2,3-di-O-methanesulfonyl-α-D-glucopyranosides

Abstract

The elimination of vicinal sulfonyloxy groups fro111 methyl 2,3-di-O-n1ethanesulfonyl-a-~-gIucopyranosides with the formation of hex-2-enopyranosides using potassium iodide, and zinc in refluxing dry dimethyl formamide has been investigated. The specific use of a zinc-copper couple has been found to be highly advantageous to the yield and reproducibility of the reaction, and the elimination proceeds successfully whether acid or base labile groups are present at carbon-4 or -6. Both the 4,6-di-0-benzoyl (3b) and the 6-0-benzoyl (3d) precursors give methyl 6-O-benzoyl-r-~-ery1ht~-11ex-2-enopyrano~ide ( 4 4 as the major product, the latter also being obtainable by selective benzoylation of methyl a-D-eqzrktohex-2-enopyranoside (4c). The reaction of the dibenzoate therefore occurs with some deacylation at carbon-4, but it is noteworthy that this is not accompanied by any epimerization. A sinlilar pattern of reaction apparently occurs with the 4,6-di-0-acetyl derivative (3a). The confornlations of the starting di-0-methanesulfonyl esters are discussed and suggestions for the n.nl.r. assignments of the groups are made.

Pyranosiduloses. II. The synthesis and properties of some alkyl 2,3-dideoxy-2-enopyranosid-4-uloses

“…Carbohydrate molecules possessing ketonic (2) and olefinic (3,4) unsaturation are favorite precursors for synthesis of branched-chain and amino (5) sugars, two classes of compounds of I considerable interest because of their occurrence in many major antibiotics (6,7). Molecules possessing both types of unsaturation in conjugation are of interest in view of the array of synthetic techniques available to them (8).…”

“…3, is formed in low yield by hydrolysis of difructose glycine (13), and syrupy methyl glycosides of 3 (4 and 5) and has been prepared by acid-catalyzed elimination from enolic precursors having the appropriate anomeric configuration (14). An alternative route to 4 and 5 via the anomeric fluorides has been recently described (15).…”

Ethyl 4-iodo-2,3,4-trideoxy-α-D-threo-hex-2-enopyranoside: synthesis and dehydroiodination

“…The diol 5 was selectively benzoylated as described previously by Fraser-Reid and Boctor (14) and the product 6 converted to the methanesulfonate ester 7 in the usual way (14) and used without further purification.…”

“…The formation of these products (Scheme 2) may be rationalized by assunling that the first event is ester cleavage followed by formation of the alkoxy-aluminum complex 14. This assumption seems justified since the debenzoylated compound 9 when treated with lithium aluminum deuteride gave the same products in the same ratio.…”

“…Regarding compound 19, the oxoniurn ion 16 may be invoked to account for retention of configuration at carbon-4 (5). Ion 16 could form with great ease from 14. A route to the acyclic diol 20 is suggested in 17; the bonds being broken are all antiparallel and, furthermore, the process accounts for the geometry of the double bonds in 20. The results of the lithium alumirturn deuteride reaction, unexpected though they were, did favour the pyranoside 8 over the furanoside PI For personal use only.…”