2000 carbohydrates

carbohydratesU 0500

16 - 218Studies on the Mercury-Desilylation of Chiral Cyclopropylmethyl-silanes – A Stereocontrolled Access to Carba-Sugars. — Stereose-lective cyclopropanation of allylsilanes (I) and desilylation of the so obtainedcyclopropylmethylsilanes (III) in the presence of Hg(NO3)2 provides an anti-stereospecific access to (E)-homoallylic mercuryorganic compounds (IV). Thesilyl group plays a crucial role in cyclopropanation. Thus, cyclopropanationof allylsilanes proceeds with different stereocontrol in the presence of silyl [asin (IX)] or hydroxyl groups [as in (VI)], which allows for a stereocontrolledaccess to trisubstituted tetrahydrofurans [cf. (VIII)/(XI)]. This methodologyis successfully extended to cyclic allylsilanes like (XII), which represents astereoselective entry to carba-sugars. Cyclopropanation of silylcyclopentadiene(XII), followed by diastereoselective dihydroxylation and mercury-desilylationfurnishes an all-cis-trisubstituted cyclopentene (XVII), which can be furtherelaborated to aldehyde (XVIII). Addition of lithiated deoxyglucose (XIX)to aldehyde (XVIII) provides access to carba-disaccharides like (XX). —(LANDAIS, YANNICK; PARRA-RAPADO, L.; Eur. J. Org. Chem. (2000)3, 401-418; Lab. Chim. Org. Organomet., CNRS, Univ. Bordeaux, F-33405Talence, Fr.; EN)

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2000 carbohydrates

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