NOVELTY - Preparing 5,6,7,7a-tetrahydro-4H-thieno(3,2-c)pyridine-2-one acid (I) comprises: (a) protecting thienopyridine compound (II) in the presence of a base to give thienopyridine compound (III); (b) halogenating (III) to give thienopyridine compounds (IV) in the presence of a halogenating agent and optionally a base; (c) converting (IV) to boronic acid compounds (V) by Grignard reaction, and treating with a boronating agent in the presence of a base; (d) treating (V) with a oxidizing agent to give thiophen-2-one compound (VI); and (e) de-protecting (VI) with an organic/inorganic acid.    USE - The process is useful for preparing (I) (claimed).    ADVANTAGE - The process safely prepares (I) with high yield and devoid of any hazard in an economical and eco-friendly manner.    DETAILED DESCRIPTION - Preparing 5,6,7,7a-tetrahydro-4H-thieno(3,2-c)pyridine-2-one acid (I) of formula (IA) or (IB) and its salts or tautomer, comprises: (a) protecting amino functionality of thienopyridine compound of formula (II) or its salt by a protecting group in the presence of a base to provide thienopyridine compound of formula (III); (b) halogenating (III) to obtain thienopyridine compound of formula (IV) in the presence of a halogenating agent and optionally, in the presence of a base; (c) converting (IV) to boronic acid compound of formula (V) by subjecting to Grignard reaction, followed by treatment with a boronating agent, in the presence of a base and subsequent hydrolysis with a acid and extraction with a solvent; (d) treating (V) with a oxidizing agent to provide the thiophen-2-one compound (VI) of formula (VIa) or (VIb); and (e) de-protecting (VI) with an organic or an inorganic acid as de-protecting agent, where organic acid salts comprise acetic acid, methanesulfonic acid, formic acid, benzenesulfonic acid, para toluene sulfonic acid or trifluoroacetic acid.    Rp = protecting group such as trityl, carbobenzoxy, tert-butyloxycarbonyl, methoxycarbonyl, ethoxycarbonyl, aliphatic or aromatic acyl;    HX = HCl, H2SO4, HBr or H3PO4; and    R1, R2 = H, CH3, C2H5, n-propyl, iso propyl, butyl, isobutyl or n-butyl.