PURPOSE: To obtain the subject compound having an antiviral activity and especially useful for AIDS by reacting a specific compound with an organic halogenocompound, treating the reaction product with a diester of an azodicarboxylic acid and phosphine, etc., opening ring and deblocking.

CONSTITUTION: A compd. of formula I (R1 is H, alkyl, alkoxy, hydroxyalkyl or halogen) is reacted with a derivative of the formula of R2X [R2 is trithyl, (1-3C mono- or dialkoxy), trithyl, pixyl, (R3R4R5)Si (R3-R5 are each 1-5C alkyl)] to obtain a compd. of formula II. This compd. is converted by the action of a diester of an azodicarboxylic acid and phosphine or a phosphite derivative in a solvent to obtain a compd. of formula III. The ring of this compound is opened in a solvent in the presence of a metal azide to obtain a compd. of formula IV and the subject compd. of formula V is obtained by deblocking the 5' functional group thereof.