1998 carbohydrates

carbohydratesU 0500

34 - 252Stereocontrolled Synthesis of α-C-Galactosamine Derivatives viaChelation-Controlled C-Glycosylation. — Treatment of sulfone (I)with ketones or aldehydes in the presence of SmI2 leads to the title compounds(III) with unexpectedly predominant 1,2-cis stereochemistry (83-95% diastere-oselectivity). This result is contrary to the previously observed trans selectivitywith glucosyl, galactosyl, and mannosyl pyridyl sulfones. The configuration atthe acyclic stereocenter of α-diastereomers (IId)-(IIf) is assumed to be S with83-86% selectivity. Other galactosyl sulfones such as (IV) and (VI) with varyingC-2 substituents form the β-anomer (V) only or no corresponding productsin the case of (VI). These results unveil an important directing effect of theC-2 acetamido group in compound (I). — (URBAN, D.; SKRYDSTRUP, T.;BEAU, J.-M.; J. Org. Chem. 63 (1998) 8, 2507-2516; Lab. Synth. Biomol.,CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.; EN)

1