To lithium diisopropylamide in 50 ml of tetrahydrofuran, prepared from 2.25 ml of diisopropylamine and 10 ml of 1.6 N n-butyl lithium in hexane at -70° under nitrogen, is added 2.0 g of thianapthene in 20 ml of tetrahydrofuran while stirring. After 1 hour, the solution of 2.65 g of 2-[2-(4-oxopiperidino)-ethyl]-1,4-benzodioxan in 20 ml of tetrahydrofuran is added and, after standing overnight, the mixture is decomposed with 9 ml of saturated aqueous ammonium chloride. The organic phase is separated, dried, evaporated, the crystalline residue washed with water and recrystallized from ethanol-acetone, to yield the 2-[2-(4-hydroxy-4-(2-benzothienyl)-piperidino)-ethyl]-1,4-benzodioxan melting at 175°-178°.
