The thermal Claisen rearrangement of theZ-isomer (5-Z) of 3,5,6-trideoxy-1,2-O-isopropylidene-3-C-methyl-α-D-ribo-hept-5-eno-1,4-furanose with triethyl orthoacetate in the presence of propionic acid gave two rearrangement products with a high level of diastereoselectivity (approximately 8.5 to 1). On the other hand, the re-arrangement executed by using theE-isomer resulted in the formation of the products without significant stereoselectivity (approximately 1.6 to 1 ratio). TheS-configuration for the newly introduced stereogenic center in the major product was secured by chemical correlation with our previously reported compound, which was the major rearrangement product of 5,6-dideoxy-1,2-O-isopropylidene-α-D-ribo-hept-5-eno-1,4-furanose. The transition state argument applied to the similar models accounts well for the stereoselectivity observed in the case of 5-Z.