Determination of the configurations of tertiary alcoholic centers in branched-chain carbohydrate derivatives : PMR spectroscopy with a lanthanide shift-reagent

Examination of the PMR spectral changes (expressed as shift gradients of individual protons) wrought by graduated addition of the paramagnetic lanthanide complex tris [1,1,1,2,2,3,3-heptafluoro- 7,7-dimethyloctane-4,6-dionato]europium(III) [Eu(fod)₃] permitted assignment of the configuration at tertiary alcoholic centers of certain sugar derivatives. The configurations of the tertiary position of 3- C-(1,3-dithian-2-yl)-1,2:5,6-di-O-isopropylidene-α-d-allofuranose (1), lethyl of 4,6-O-benzylidene-2- deoxy-3-C-(dithian-2-yl)-α-d-ribo-hexopyranoside (2) and the corresponding 3-C-butyl compound (2a), and methyl 2-C-(1,3-dithian-2-yl)-3,4-O-isopropylidene-δ-d-ribopyranoside (3) were assigned by comparison with reference spectra. The proton shift-gradients for 5-C-benzoyloxymethyl-2,3-O- cyclohexylidene-1-O-p-tolylsulfonyl-1(R),2(S),3(S),5(R)-cyclohexanetetrol (4), taken in conjunction with the spin-spin coupling values, permit direct assignment of relative stereochemistry in the latter compound.