Stereochemical Studies. XLV. A Novel Regiospecific Ring Opening of optically Active 2-Substituted-1-tosylaziridines

Abstract

In the course of our examinations on an applicability of the novel synthetic scheme for optically active pyrrolidines from L-α-amino acids, it was found that the reaction of (R) (-)-2-phenyl-1-tosylaziridine ((R) (-)-9) with diethyl potassiomalonate exclusively afforded (S) (+)-pyrrolidine-3-carboxylate ((S) (+)-10) as a mixture of two diastereoisomers by the attack of malonate anion at the C₂-carbon of the aziridine ring. This result is completely different from those obtained for (S)-2-benzyl or isopropyl-1-tosylaziridine ((S)-7a, b) on which the attack of malonate anion occurred specifically at the unsubstituted C₃-carbon. These results clearly show that electronic effect of the C₂-substituent is considered as the most important factor which controls regiospecificity of the ring opening of 2-substituted-1-tosylaziridines by malonate anion. Structual confirmation of (S) (+)-10 was also carried out by converting it into (S) (+)-3-phenylpyrrolidine ((S) (+)-17).