[6-O-(1,2:3,4-Di-O-isopropylidene-alpha-D-galactopyranosyl)methyl]tin derivatives

A family of [6-O-(1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranosyl)methyl]tine species Ph(n)Sn(CH(2)OR)(4-n) (1n = 1-3), Ph(n)Me(3-n)Sn(CH(2)OR) (2n = 0-3) and Bu(3)SnCH(2)OR (3) have been prepared from 1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose (ROH) and the iodomethyltin compounds Ph(n)Sn(CH2I)(4-n) (n = 1-3), Ph(n)Me(3-n)SnCH(2)I (n = 1-3) and Bu(3)SnCH(2)I. The pyranose rings in these mono-, di- and trisaccharide derivatives, as well as in IPh(n)Sn(CH(2)OR)(3-n) (4n = 0-2) and IPh(n)Me(2-n)Sn(CH(2)OR) (5n = 0, 1), have similar twist-boat conformations in solution. The solution delta(119)Sn NMR values for the series (1n = 1-4) and (4n = 1-3) do not vary linearly with n, The X-ray diffraction study of (4n = 1) at 120 K revealed that only one of the sugar moieties acts as a C,O-bidentate ligand, via its pyranose ring oxygen. The tin centre in solid (4n = 1) is five-coordinate and has a trigonal bipyramidal geometry: the Sn-O and Sn-I bond lengths are 2.759(5) and 2.790(2) Angstrom respectively, with the I-Sn-O valency angle of 173.5(1)degrees. As indicated by the solid state and solution delta(119)Sn values (-177.8 and -130.7 ppm respectively), the solid state structure of (4n = 1) does not survive on dissolution. The two pyranose rings in solid (4n = 1) have similar conformations (intermediate between screw-boat degrees S-5 and the twist-boat forms degrees T-2, with deviations in the direction of the boat-form B-2,B-5). Compound (1n = 3) undergoes transmetallation with PhLi to give LiCH(2)OR, which was trapped as the triphenylgermanium derivative Ph(3)GeCH(2)OR.