ASYMMETRIC CYCLIZATIONS OF SOME CHLOROHYDRINS CATALYZED BY OPTICALLY ACTIVE COBALT (SALEN) TYPE COMPLEXES

Article abstract of DOI:10.1016/0040-4020(80)80189-X

Optically active chloromethyloxirane was obtained from 1,3-dichloro-2-propanol by a process of asymmetric synthesis.The highest enantiomeric excess (e.e.) of chloromethyloxirane that could be obtained was 67percent, using Co(II) (3,5-Cl,Cl-sal)2(S-CHXDA) and K2CO3 as the catalyst and base, respectively.For purpose of comparison, asymmetric cyclizations of racemic 2,3-dichloro-1-propanol and 2-chloro-1-propanol were examined; optically active chloromethyloxirane and methyloxyrane were obtained according to kinetic resolution mechanisms, although the optical purities of oxiranes formed were not so high.The mechanisms for the asymmetric reactions were investigated by circular dichroism and absorption spectroscopies.It was found that the cobalt (salen) type complex forms a new complex with alkali metal carbonate, similarly to the function of crown ether.The substrate interacts with the newly formed chiral complex, followed by cyclization to give optically active oxiranes.