Patent ID: 7649114

Claim:
A method for isolating a stereoisomer from a mixture comprising the two stereoisomers of formulas I-A and I-A′ or the two stereoisomers of formulas I-B and I-B′ or all four stereoisomers of formulas I-A, I-A′, I-B and I-B′ wherein R 1 , R 2 and R 3 are each independently selected from the group consisting of —H, —F, —Cl, —C 1 -C 6 -alkyl, —S—C 1 -C 6 -alkyl, —OH, —O—C 1 -C 6 -alkyl, —O—C 1 -C 6 -alkylenephenyl, —OCO—C 1 -C 6 -alkyl, —OCO 2 —C 1 -C 6 -alkyl, —OCON(C 1 -C 6 -alkyl) 2 and —O—SiR 8 R 9 R 10 , wherein R 8 , R 9 and R 10 are each independently selected from the group consisting of —C 1 -C 6 -alkyl and -phenyl; R 4 is —H or —C 1 -C 6 -alkyl; R 5 is —C 1 -C 6 -alkyl; and R 6 and R 7 , are each independently selected from the group consisting of —H and —C 1 -C 6 -alkyl; or salts thereof with organic or inorganic acids; said method comprising: (a) manipulating the mixture ratio of the stereoisomers in the mixture so that at least one of the stereoisomers is present in an enantiomeric excess, and (b) adding phosphoric acid under conditions which bring about precipitation of the stereoisomer present in enantiomeric excess from a solution as phosphate, hydrogenphosphate or dihydrogenphosphate.