The application of organocatalytic asymmetric epoxidation

• Main Author: Alahmdi, Mohammed
• Published: University of East Anglia 2014
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.630126

In the field of research of target natural product synthesis, catalytic asymmetric synthesis has become a vital tool to obtain enantiomerically pure compounds, and is often used in the synthesis of natural products as a key step.1 For example, the asymmetric dihydroxylation was used in synthesis of gibberellic acid (GA3)2 by E. J. Corey, who was awarded the Nobel Prize for his developments in the theory and methodology of organic synthesis.2 This thesis is based on an ongoing research in the area of catalytic asymmetric synthesis that has been carried out in our group. Since 2005, metal-free catalytic asymmetric epoxidation using iminium salts such as 1 has been successfully employed to access chiral chromenes within the Page group. Iminium-catalysed asymmetric epoxidation methodology has been applied to the synthesis of levcromakalim, 3 trans-khellactone, and lomatin,4 which are based on a chromene-type structure. In this thesis, we offer a detailed discussion on the influence of iminium salts on flav-3-ene derivatives and their stability under oxidative conditions. We were also able to successfully apply our methodology towards the enantioselective total synthesis of (3S,4R)-trans-3,4-dihydroxy-3,4-dihydromollugin 2. The key epoxidation step proceeded in 70.4% ee and high yield, using chiral iminium salt catalyst 1 under aqueous conditions. The acid-catalysed epoxide ring-opening of epoxide 4 afforded trans-diol 3 in high yield.