PURPOSE: To obtain the subject intermediate useful in the production of nojirimycins for use as antidiabetics, etc., industrially advantageously by reducing 5-azido-5-deoxy-1,2,-O-isopropylidene-α-D-glucuronolactone with a hydride reducing agent.

CONSTITUTION: 5-Azido-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone represented by formula I is dissolved in anhydrous tetrahydrofuran and reduced with a hydride reducing agent (e.g. lithium aluminum hydride) to obtain 5- amkino-5-deoxy-1,2-O-isopropylidene-α-D-glucofranose represented by formula II. This is reacted with aqueous sulfur dioxide top form nojirimycin bisulfite, and this is quantitatively converted into nojirimycin by interconversion.