A facile and efficient method for the kinetic separation of commercially available cis- and trans-limonene epoxide

Abstract cis - and trans -Diastereomers of ( R )-(+)-limonene oxide can be purified by simple kinetic separation of the commercially available (1:1) diastereomeric mixture of limonene oxides. Nucleophilic amines, such as pyrrolidine and piperidine, selectively open the epoxide ring of the trans -isomer, leaving the cis -limonene oxide largely unreacted. The unreacted cis -( R )-limonene oxide is recovered in up to 88% yield. On the other hand, less nucleophilic amines, such as triazole or pyrazole, selectively catalyze hydrolysis of the cis -limonene oxide to 1,2-limonene diol leaving the trans -limonene oxide largely unreacted. The unreacted trans -limonene oxide is recovered in up to 80% of the theoretical yield by a simple workup procedure. The cis - and trans -diastereomers of ( R )-(+)-limonene oxide thus isolated were found to be >98% pure by both GC and NMR analyses. Thus, depending on the choice of amine, either cis - or trans -limonene oxide may be obtained in high diastereomeric purity by this simple and environmentally friendly method.