Patent ID: 6846935

Claim:
A method of preparing an enantiomerically pure compound with the formula 1 wherein each of R 1 and R 3 which may be the same or different is selected from the group consisting of hydrogen, chlorine, fluorine, methyl, trifluoromethyl and methoxy; and each of R 2 and R 4 which may be the same or different is selected from the group consisting of hydrogen, chlorine, fluorine, methyl, trifluoromethyl, methoxy, trifluoromethoxy, methylsulphonyl and aminosulphonyl; with the condition that one of the substituents R 2 or R 4 is a methylsulphonyl or aminosulphonyl group; said method comprising: (a) reacting a racemic mixture of a compound with formula (±)-8 wherein each of R 1 and R 3 which may be the same or different is selected from the group consisting of hydrogen, chlorine, fluorine, methyl, trifluoromethyl and methoxy; and each of R 2 and R 4 which may be the same or different is selected from the group consisting of hydrogen, chlorine, fluorine, methyl, trifluoromethyl, methoxy, trifluoromethoxy, methylsulphonyl, aminosulphonyl and sodium sulphonate; of condition that one of the substituents R 2 or R 4 is a sodium sulphonate group, with optically active ephedrine, to form a mixture of sodium salts of the following two enantiomer: diastereoisomeric salts (−)-8·(−)-ephedrine and (+)-8·(−)-ephedrine: (b) separating the enantiomerically pure sodium salts; and (c) reacting said mixture of sodium salts of each enantiomer with thionyl chloride followed by either: ammonium carbonate or ammonia; or sodium sulphite and either methyl iodide or methyl sulphate.