“…Isomerization of a sample of 221 In chloroform-d, saturated with hydrogen chloride, resulted in the formation of 222, with an exomethyl group, to the extent of 18% as indicated by 1H NMR spectroscopy. It has also been reported177 that, on treatment with methanolic hydrogen chloride, 2,4-O-ethylldene-o-erythrose (224) rearranges to give mainly methyl 2,3-O-ethylidene-/3-D-erythrofuranoslde (226). Likewise with dilute aqueous acid 2,3-0-ethylidene-/3-D-erythrofuranose (227) dence was obtained for the configuration at the ethylidene acetal carbon atom, but the related rearrangement113 of 2,4-O-benzylidene-o-erythrose (225) gave 228 with the phenyl group endo.…”