Carbocyclische Verbindungen aus Monosacchariden. I. Umsetzungen in der glucosereihe

Abstract

A method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5-bromo-5-deoxyglucosides (such as 10, 17 and 23, see Scheme 3) with Zn or butyl lithium yielding 5,6-dideoxy-hex-5-enoses (such as 11 a.nd 24, see Schemes 3 and 4 ) , and the subsequent cyclization of these hexenoses with N-methyl-or N-(alkoxyalky1)hydroxylamines (via the corresponding nitroines) to form cyclopentano-isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano-isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62. The configuration of the cyclization products were established1 by pyrolysis of the N-oxide 65 to the enol ether 67 (Scheme 10).

Domino Knoevenagel hetero Diels-Alder reactions of sugar derived δ,ε-unsaturated aldehydes

“…Lower reactivity for this 1,3-dicarbonyl component was expected and was indeed observed since all reactions run gave no cycloaddition products. In fact, similar results were obtained by Vasella's group 15 when DKHDA reaction of 8 to 6 was attempted leading to a double addition of dimedone to the unsaturated aldehyde.…”

Diene, Enyne, and Diyne Metathesis in Natural Product Synthesis

“…Carbohydrate carbocyclization based on a sequence of Vasella reductive opening of iodo-substituted methyl glycosides [25], and RCM of the dienes available from the resulting unsaturated aldehydes, were used to prepare a series of natural compounds (Schemes 5-7).…”

“…The highly functionalized diene 35 was prepared from iodo compound 34 via Vasella-type reductive ring opening [25], followed by Julia-Kocienski methylenation of the resulting aldehyde. The ring closure to cyclopentene 36 in the presence of Hoveyda's highly active ruthenium catalyst D proceeded smoothly (benzene, DT, 14 h), notwithstanding the presence of the urethane and sulfonamido groups in 35.…”

Synthesis of (+)-(1S,2S,5R,6S)-1-Hydroxysamin froml-(+)-Arabinose

“…Dihydroxy olefin 18 was produced by reductive ring opening with zinc 20 ) in refluxing ethanol in a 93 % yield. Protection of the primary and tertiary hydroxy groups as a benzoyl ester and triethylsilyl ether, respectively, and subsequent treatment of 20 with potassium carbonate in methanol gave hydroxy olefin 21 in a 76% overall yield from 18.…”