C-stannylated carbohydrate derivatives. Part 3. 1,2 : 5,6-Di-O-isopropylidene-3-C-(organostannyl)methyl-α-D-allofuranose derivatives. Crystal and molecular structure of 3-C-(dibutyliodostannyl)methyl-1,2 : 5,6-di-O-isopropylidene-α-D-allofuranose
Abstract
Reaction of R2R′SnCH2Li(R = R′= Me or Bu) with 1,2 : 5,6-di-O-isopropylidene-α-D-ribohexofuranos-3-ulose provides 1,2 : 5,6-di-O-isopropylidene-3-C-(R2R′Sn)methyl-α-D-allofuranose (5): the glucose isomer was not obtained. Despite a hydroxy group being in a β- position to tin in compound (5), no β-elimination products are obtained on reaction with CF3CO2H, reaction proceeding instead at the C(5)–C(6) protecting group. Cleavage of an alkyl–tin bond in (5) by iodine is aided by nucleophilic assistance of the β-hydroxy group. 1H N.m.r. spectra of (5; R = Me, R′= I) in CDCl3 indicate the formation of a four-membered chelate ring due to SnOH interaction. The crystal structure of (5; R = Bu, R′= I) was determined; there is a distorted trigonal bipyramidal arrangement about tin with I and O axial; Sn—O 2.68(2)Å.