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

Article abstract of DOI:10.1016/0022-328x(96)06141-4

A family of [6-O-(1,2:3,4-di-O-isopropylidene-α-D-galactopyranosyl)methyl]tin species Ph_nSn(CH₂OR)_4-n (1n = 1-3), Ph_nMe_3-nSn(CH₂OR) (2n = 0-3) and Bu₃SnCH₂OR (3) have been prepared from 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (ROH) and the iodomethyltin compounds Ph_nSn(CH₂I)_4-n (n = 1-3), Ph_nMe_3-nSnCH₂I (n = 1-3) and Bu₃SnCH₂I. The pyranose rings in these mono-, di-and trisaccharide derivatives, as well as in IPh_nSn(CH₂OR)_3-n (4n = 0-2) and IPh_nMe_2-nSn(CH₂OR) (5n = 0, 1), have similar twist-boat conformations in solution. The solution δ¹¹⁹Sn 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) A? respectively, with the I-Sn-O valency angle of 173.5(1)°. As indicated by the solid state and solution δ¹¹⁹Sn 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 °S₅ and the twist-boat forms °T₂ with deviations in the direction of the boat-form B_2,5). Compound (1n = 3) undergoes transmetallation with PhLi to give LiC0H₂OR, which was trapped as the triphenylgermanium derivative Ph₃GeCH₂OR.