A process for the preparation of 5-[2-cyclopropyl-1-(2-fluorophenyl)-2-oxoethyl]-4,5,6,7-tetrahydrothieno[3,2-c]pyridine-2-yl acetate (prasugrel) of Formula including the following steps: a) (2-fluorophenyl)-acetic acid of Formula is reacted in the presence of a base with cyclopropane carboxylic acid ethyl ester of Formula, b) then the obtained 1-cyclopropyl-2-(2-fluorophenyl)ethanone of Formula is brominated to obtain 2-bromo-1-cyclopropyl-2-(2-fluorophenyl)ethanone base of Formula, c) N-trityl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine of Formula (VIII) is reacted with hexyllithium, then tributyl-borate, finally with hydrogen-peroxide, to form 5,6,7,7a-tetrahydrothieno[3,2-c]pyridine-2 -one hydrochloride of Formula, d) the 2-bromo-1-cyclopropyl-2-(2-fluorophenyl)ethanone base of Formula in the presence of sodium carbonate is reacted with 5,6,7,7a-tetrahydrothieno[3,2- c]pyridine-2(4 H)-one hydrochloride of Formula, to obtain the 5-[α-cyclopropyl carbonyl-2-fluorobenzyl)-2-oxo-2,4,5,6,7,7a-hexahydro-thieno[3,2-c]pyridine of Formula, e) the compound of Formula is acetylated and the so obtained crude 5-[2-cyclo-propyl-1-(2-fluorophenyl)-2-oxoethyl]-4,5,6,7-tetrahydrothieno[3,2-c]pyridine-2-yl acetate (prasugrel) of Formula is prepared, f) finally in a purification step the crude prasugrel is converted into a purified prasugrel product by removing a bromopentyl impurity of Formula from 5-[2-cyclopropyl-1-(2-fluorophenyl)-2-oxoethyl]-4,5,6,7-tetrahydrothieno[3,2-c]-pyridine-2-yl acetate (prasugrel) of Formula wherein said impurity is converted to an easily removable high-polarity quaternary ammonium iodide of formula (Xb) and wherein the use of ether solvents are excluded from each step of the process. a) (2-fluorophenyl)-acetic acid of Formula is reacted in the presence of a base with cyclopropane carboxylic acid ethyl ester of Formula, b) then the obtained 1-cyclopropyl-2-(2-fluorophenyl)ethanone of Formula is brominated to obtain 2-bromo-1-cyclopropyl-2-(2-fluorophenyl)ethanone base of Formula, c) N-trityl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine of Formula (VIII) is reacted with hexyllithium, then tributyl-borate, finally with hydrogen-peroxide, to form 5,6,7,7a-tetrahydrothieno[3,2-c]pyridine-2 -one hydrochloride of Formula, d) the 2-bromo-1-cyclopropyl-2-(2-fluorophenyl)ethanone base of Formula in the presence of sodium carbonate is reacted with 5,6,7,7a-tetrahydrothieno[3,2- c]pyridine-2(4 H)-one hydrochloride of Formula, to obtain the 5-[α-cyclopropyl carbonyl-2-fluorobenzyl)-2-oxo-2,4,5,6,7,7a-hexahydro-thieno[3,2-c]pyridine of Formula, e) the compound of Formula is acetylated and the so obtained crude 5-[2-cyclo-propyl-1-(2-fluorophenyl)-2-oxoethyl]-4,5,6,7-tetrahydrothieno[3,2-c]pyridine-2-yl acetate (prasugrel) of Formula is prepared, f) finally in a purification step the crude prasugrel is converted into a purified prasugrel product by removing a bromopentyl impurity of Formula from 5-[2-cyclopropyl-1-(2-fluorophenyl)-2-oxoethyl]-4,5,6,7-tetrahydrothieno[3,2-c]-pyridine-2-yl acetate (prasugrel) of Formula wherein said impurity is converted to an easily removable high-polarity quaternary ammonium iodide of formula (Xb) and wherein the use of ether solvents are excluded from each step of the process.