For synthetic and st~reochemical studies in the methyl tetroside series, we needed methyl 2,3-anhydro-a-L-erythrofuranoside
(1) and methy 2,3-anhydro-/3-r.,-e~throfuranoside
(2) (or the corresponding D enantiomers). Only the racemic epoxides 1 and 2 have been prepared by Gagnieu et ali, using epoxidation of 2-methoxy-2,5_dihydrofuran with peroxybenzimidic acid. We now report on new syntheses of the optically active oxiranes 1 and 2, starting either from 1,20isopropylidene-3-U-~-toluenesulfonyi-~-~-threofuranose
(3) or methyl cu-D-threofuranoside (4) and its j3 anomer 5.
Methanolysis of the 3-O-p-toluenesulfonyl derivative 3 (the sign of the specific rotation of 3 was incorrect in our previous paper21 in the presence of a strongly acidic ion-exchange resin for 30 h gave a mixture containing methyl 3-0-ptoluenesulfonyl-tu-D-threofuranoside (6) and its /3 anomer 7 in 72% yield (ratio 1.3 : 1) in addition to unreacted starting material 3. Prolonged treatment of 3 could not be used to increase the yield of 6 and 7 due to the concomitant solvolysis of the p-toluenesulfonyl group in the methyl threofuranosides 6 and 7. The configuration at the anomeric centre was assigned to the new methyl glycosides on the basis of "H NMR spectra. The larger .11,2 coupling of 7 (4.5 Hz) indicates, in a furanose series, the 1,2-c& arrangement3-5, i.e., the P-D configuration, whilst the Jr,, coupling of 1.2 Hz clearly designates the LY anomer 6. IR spectra also support this assignment. The stretching vibration of the hydroxyl group of 7 provides in the spectrum a sharp band at vmax 3560 cm-' corresponding to a strong hydrogen bond to O-l. The measured value is almost the same as for the corresponding