Synthesis of a 4,5-unsaturated-3-keto sugar (methyl 2-O-benzoyl-4-deoxy-6-O-triphenylmethyl-α-D-glcero-hex-4-enopyranosid-3-ulose)

Abstract

. Can. J. Chem. 56,2221Chem. 56, (1978. An approach to the synthesis of the hex-4-enopyranosid-3-ulose 5 has been investigated. T h e readily available 3-keto derivative 8 is easily debenzylidinated but the resulting diol is benzoylated preferentially at carbon 4 rather than at the primary position. However, tritylation occurs at the primary position and the product is sulfonylated to give the 4-0-methylsulfonyl derivative (llb). Iodinolysis of this a-ketosulfonate did not follow an SN2 course giving the desired axial iodide 14b. Instead a course of reductive elimination was observed involving the presumed intermediacy of an enolic hypoiodite. B elimination of methanesulfonic acid from l l b was in fact possible by using diazabicyclononene in benzene-tetrahydrofuran solution. T h e process undoubtedly involves epimerisation, and the product consists of a mixture of the desired 5 (R = CPh,) and its 2-epimer 22. These enones are prone to base-catalysed decomposition so that although the three steps from the starting ketone 8 to the sulfonate l l b can each be carried out in excellent yield, the final elimination proceeds in 3 9 x yield after isolation.MARK BERNARD YUNKER et BERT FRASER-REID. Can. J. Chem. 56,2221Chem. 56, (1978.On a CtudiC une approche a la synthese des hexeno-4 pyrannosiduloses-3 (5). On peut facilement enlever le groupe benzylidene du derive ctto-3 (8) facilement accessible mais le diol qui en resulte est benzoyle preftrentiellement au niveau du carbone-4 plut6t que dans la position primaire. Toutefois la tritylation se produit en position primaire et le produit peut Etre sulfonylC pour obtenir le dtrivt 0-methylsulfonyl-4 (llb). L'iodolyse de cet a-cetosulfonate ne se produit pas suivant un mecanisme SN2 pour conduire a I'iodure axial dtsirt (14b). I1 se produit plut6t une elimination reductrice impliquant vraisemblablement un hypoiodure enolique comme intermtdiaire. L'tlimination B de I'acide methanesulfonique a partir de ( l l b ) est possible si I'on fait appel au diazabicyclononene dans une solution de benzene-tttrahydrofuranne. Le processus implique sans aucun doute une tpimtrisation et le produit comporte un melange d u produit (5) desire (R = CPh,) et de son tpimere-2 (22). Ces enones peuvent subir facilement des dCcompositions catalysees par les bases; ceci implique que m@me si trois ttapes peuvent Etre effectuees, avec de bons rendements, a partir de la cttone (8) pour conduire au sulfonate ( l l b ) , l'elimination finale ne se produit qu'avec un rendement de 3 9 z en produit isole. [Traduit par le journal]The synthesis and reactions of unsaturated pyranosides have long been an area of interest in this laboratory (1) and in pursuing this interest we have developed and published preparative procedures for the enones 1 (2a; see also 2b and earlier work by P. M. Collins), 2 (3), and 3 (4). The unsaturated lactone 4 has also been prepared in our laboratory2 and hence the potential exists for carrying out conjugate addition reactions at carbons 1, 2, 3, and 4. Indeed many of these enones...

A New Reaction for the Direct Conversion of 4-Azido-4-deoxy-d-galactoside into a 4-Deoxy-d-erythro-hexos-3-ulose

“…Various derivatives of 4-deoxy- d - erythro -hexos-3-ulose ( 1 ) are useful intermediates for the chemical synthesis of natural and unnatural carbohydrate mimetics − and natural products such as amipurimycin − and miharamycin. , Compound 1 and related species have traditionally been prepared by the oxidation and deoxygenation of sugars 3,4 or by the Diels−Alder reaction of aldehydes and dienes. , This paper reports a novel method for preparing a protected form of 1 , namely, methyl 2,6-di- O -benzyl-4-deoxy-α- d - erythro -hexopyranosid-3-ulose ( 2 ), from methyl α- d -glucopyranoside ( 3 ). A new reaction has been invented for removing the azido group and oxidizing the hydroxyl group of methyl 4-azido-2,6-di- O -benzyl-4-deoxy-α- d -galactopyranoside ( 4 ) in one step to afford the synthetic target 2 .…”