Patent ID: 8569491

Claim:
A method for preparing entecavir of formula (I), comprising the steps of: (a) hydrolyzing an α-exomethylene derivative of formula (II) to obtain a compound of formula (III); (b) carrying out a Mitsunobu reaction of the compound of formula (III) with a purine derivative of formula (IV) to obtain a nucleoside compound of formula (V); (c) subjecting the nucleoside compound of formula (V) to a reaction with tetrabutyl ammonium fluoride to obtain a compound of formula (VI); and (d) hydrolyzing the compound of formula (VI): wherein R 1 and R 2 are each independently a hydroxy-protecting group, or R 1 and R 2 are fused together to form a cyclic hydroxy-protecting group; R 3 is benzoyl or arylbenzoyl; and X is halogen or benzyloxy.