PURPOSE: The reduction of (chlorobenzoyl)-tetrahydro-thienopyridine is reduced with sodium borohydride in an acidic dimethylsulfoxide enables the advantageous production of the titled compound which is used as a blood platelet coagulant or a blood platelet adhesion inhibitor.

CONSTITUTION: The reduction of 5-(2-chlorobenzoyl)-4,5,6,7-tetrahydro-thieno[3,2- C]pyridine of formula I is carried out with sodium borohydride, preferably in an amount of 1W4 times the molar quantity of the pyridine in an acidic dimethylsulfoxide to give the objective 5-(2-chlorobenzyl)-4,5,6,7-tetrahydro- thieno[3,2-C]pyridine. The acidic dimethylsulfoxide is prepared by adding methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid or p- toluenesulfonic acid.