Enantiomeric separation of cyclopropane derivatives on a polysaccharide-based chiral stationary phase

The enantioseparation of a set of new cyclopropanes derived from Meldrum's acid, dimethyl malonate, (silanoxyvinyl)-diazoacetates and 3,3,3-trifluoro-2-diazopropionate has been achieved on cellulose tris(3,5-dimethylphenylcarbamate) Chiralcel OD coated on 10 μm silica-gel as chiral stationary phase in high-performance liquid chromatography (HPLC). The HPLC was equipped with a sensitive optical rotation detector for monitoring the optical activity of the racemic and enantioenriched cyclopropanes prepared via the Rh(II)-catalyzed asymmetric intermolecular cyclopropanations. The mobile phase was a mixture of n-hexane-2-propanol (90:10, or 99:1, v/v) with a flow-rate of 0.3 ml/min. The UV detector was set at 254 nm. The advantages of the liquid over the gas chromatographic analysis of the cyclopropanes are demonstrated by a comparative study of both methods. The methods provide an easy and direct determination of the enantiomeric excesses of the cyclopropanes.