A Sharpless asymmetric dihydroxylation of the commercially available building block 1 affords the common chiral intermediate 2 for the synthesis of the fluorinated monosaccharides 3–5 (Bn=benzyl).
A perfluoroalkylidene lithium mediated cyclisation approach for the enantioselective synthesis of a tetrafluorinated aldose (ribose) and of a tetrafluorinated ketose (fructose), both in the furanose and in the pyranose form, is described.
A short synthesis of the homochiral disubstituted butenolide 1 is described in four steps from arabitol. The key steps are the selective kinetic protection of arabitol and the cyclization of 11 to form the butenolide ring. This last transformation represents a rare example of a fully stereoselective cyclitive desymmetrization process of a "pseudo"-C2-symmetric substrate.
On the basis of our previously described selective protection of arabitol as its 1,2:4,5-bis-pentylidene acetal 5, we report a straightforward synthesis of the novel "pseudo"-C(2)-symmetric 3-azido-1,2:4,5-diepoxypentane building block 4 in 6 steps from arabitol. Using a similar synthetic route, an improved synthesis of the C(2)-symmetrical 1,2:4,5-bis-epoxypentane building block 1 is described, also in 6 steps from arabitol. Both enantiomers of 1 and 4 are accessible, and all reactions involved are easily amenable for large-scale synthesis.
[reactions: see text] A concise synthesis of highly functionalized cyclopentane derivatives via a Brook rearrangement mediated stereoselective linchpin cyclization reaction involving tert-butyldimethylsilyl-1,3-dithianyllithium and homochiral 1,4-bis-epoxides is described.
Carbohydrates U 0500Enantioselective Synthesis of Tetrafluoroethylene-Containing Monosaccharides.-A straightforward synthesis of a furanose (VII), a pyranose (X) and a glycal (XI) containing a tetrafluoroethylene unit is presented using a fluorinated-building-block approach. The approach starts with the asymmetric Sharpless dihydroxylation of a terminal tetrafluorinated alkene (I) followed by an appropriate cyclization step. A novel domino perfluoroalkyl radical addition-atom transfer-nucleophilic cyclization reaction is developed for the formation of the pyranose ring (X). -(BOYDELL, A. J.; VINADER, V.; LINCLAU*, B.; Angew.
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