The preparation of the enantiomerically pure duloxetine intermediate (S)-AT-OL by its chiral resolution is exemplified in U.S. Pat. No. 5,362,886 (U.S. '886) and in WO 2004/031168, by the use of (S)-(+)-mandelic acid and (−)-2,3:4,6-Di-O-isopropylidene-2-keto-L-gulonic acid, respectively. The U.S. '886 patent describes the preparation of duloxetine by the chiral resolution of N,N-Dimethyl-3-(2-thienyl)-3-hydroxypropanamine (rac-AT-OL) with (S)-mandelic acid (Stage a), its reaction with fluoronaphtalene (Stage b) to give N,N-Dimethyl-3-(1-naphthalenyloxy)-3-(2-thienyl)propanamine (DNT), demethylation with phenyl chloroformate (Stage c), basic hydrolysis in the presence of (Stage d), and acidification (Stage e) in accordance with the following Scheme 1.
