ABSTRACT
Experimental Methods ............................................................................................. 16 General Methods ................................................................................................. 16
Methyl 2,6-Di-O-Benzyl-4-Deoxy-3-O-Naphthylmethyl-β-d-threoHex-3-Enopyranoside (13) ............................................................................. 16 Methyl 2-O-Benzyl-4-Deoxy-3-O-p-Methoxybenzyl-6-OMethoxymethyl-β-d-threo-Hex-3-Enopyranoside (15) .................................. 17 3-Azidopropyl 2-Acetamido-3,6-Di-O-Benzyl-2,4-Dideoxy-βd-threo-Hex-3-Enopyranosyl-(1 → 4)-2,3,6-Tri-O-Benzyl-β-dGlucopyranosyl-(1 → 2)-3,4-Di-O-Benzyl-α-l-Rhamnopyranoside (17) ..... 17 Methyl 3,4,6-Tri-O-Benzyl-2-Deoxy-β-d-threo-Hex-2Enopyranoside (19) ....................................................................................... 18 2-Deoxy-3,4-O-Isopropylidene-6-O-Trityl-β-d-threo-Hex-2Enopyranosyl-(1 → 4)-2,3:5,6-Di-O-Isopropylidene-Aldehydo-dGlucose Dimethyl Acetal (21) ........................................................................ 18 Methyl 3,4-Di-O-Benzyl-2,6-Dideoxy-α-l-threo-Hex-2Enopyranoside (23) ........................................................................................ 19
References ................................................................................................................26
Unsaturated sugars are useful synthetic intermediates for the conversion of common saccharides into complex carbohydrates,1 as well as for the preparation of other types of enantiomerically pure derivatives.1,2 Glycals, the cyclic vinyl ethers involving the anomeric center, are the most popular class of unsaturated monosaccharide derivatives,3 but other types of ole¥nic pyranosides are well known, for example, 2,3-dideoxy-hex-2-enopyranosides available from glycals through the Ferrier-I rearrangement.1,4 Less studied are other classes of cyclic pyranoside enol ethers having the double bond at different positions of the hexopyranose framework, with the exception of 6-deoxy-hex-5-enopyranosides, which are easily obtained by elimination reaction on C-6-activated derivatives.5 Preparation of pyranoside enol ethers by elimination of a leaving group from a secondary position has gained a preparative value only after the introduction of tri—uoromethanesulfonates (tri—ates).6 However, the use of tri—ates may be problematic, in particular (a) the dif¥cult puri¥cation of the tri—ate intermediates by chromatography and (b) a side-reaction arising from the base attack at the sulfur atom, leading to the formation of the starting alcohol.
