Patent ID: 7737273

Claim:
A process for preparation of the compound of formula I: wherein R 1 is C 1 to C 3 -alkyl or H; and R 2 is H or R—C(O)—OCH 2 — wherein R is C 1 to C 6 -alkyl or C 1 to C 6 -alkoxide; provided both the R 2 are not H; or a pharmaceutically acceptable salt thereof: which comprises: a) reacting the compound of formula II: wherein R 1 is same as defined above with an acetal of formula III: wherein R 3 is independently C 1 to C 6 -alkyl or H, wherein the said alkyl is unsubstituted or is substituted with 1 or 2 halo, cyano, nitro; R 4 is H or C 1 to C 6 -alkyl, wherein the said alkyl is unsubstituted or is substituted with 1 or 2 halo, cyano, nitro; R 5 is C 1 to C 6 -alkyl, wherein the said alkyl is unsubstituted or is substituted with 1 or 2 halo, cyano, nitro; to obtain the compound of formula IV: wherein R 1 , R 3 and R 4 are same as defined above; b) reacting the compound of formula IV with the compound of formula V: R—C(O)—O—CH 2 —Y V wherein R is same as defined above, Y is a leaving group to form protected compound of formula VI: wherein R 1 , R 2 , R 3 and R 4 are same as defined above; c) deprotecting the compound of formula VI to form the compound of formula I; and d) optionally converting the compound of formula I to a pharmaceutically acceptable salt.