| Abstract
| - Amines have previously been reported to catalyze the epoxidation of alkenes using Oxone(2KHSO5+KHSO4+K2SO4), and significant levels of asymmetric induction were observed. From screeninga series of amines based on 2-substituted pyrrolidines, it has now been found that more consistent andreproducible results are achieved with the HCl salt of the amine compared to the amine itself. Up to 66%ee was achieved in epoxidation of 1-phenylcyclohexene. The chiral amine could be reisolated in >90%yield when reactions were conducted at −10 °C, indicating that the integrity of the amine was maintainedduring the oxidation process. At −10 °C, (S)-2-(diphenylmethyl)pyrrolidine 1 reacted with Oxone to give amixture of ammonium salts containing the peroxymonosulfate salt 6b. The enantioselectivity obtained withthis salt was compared to the amine·HCl salt catalyzed process and identical results were observed,indicating that the true oxidant was the peroxymonosulfate salt 6b. The relative rates of oxidation of cis-and trans-β-methylstyrenes together with the ρ value of a series of 1-arylcyclohexenes were determined.These studies indicated that the amine catalyzed process involved electrophilic oxidation. On the basis ofthese findings, a new mechanism is advanced in which the protonated amine not only acts as a PTC butalso activates Oxone, through hydrogen bonding, toward electrophilic attack.
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