Abstract
Synthesizing pharmaceutical drugs with incorrect stereochemistry can lead to detrimental effects in one’s body. Therefore, developing a method that can yield high stereoselectivity is important in natural product and pharmaceutical drug syntheses. Epoxides are frequently used as intermediates in total synthesis of bioactive compounds due to their ability to create multiple chiral centers simultaneously, which can reduce the number of steps in a synthesis. The classic asymmetric epoxidations (Jacobsen’s and Sharpless-Vanadium epoxidation reactions) utilize metal catalysts to generate epoxides with high stereoselectivity. This research focuses on the development of optically active chiral oxovanadyl (IV) catalysts by utilizing salen ligands to offer an alternative methodology for catalytic epoxidation reactions. Vanadium catalysts are, in particular, of high interest due to their ability to effectively activate peroxides and transfer oxygen to alkenes. Eight unique oxovanadyl (IV) salen catalysts were synthesized and characterized by FT-IR and HR-ESI-MS. The catalysts were employed in various epoxidation reactions with different substrates to test for epoxide formation and stereoselectivity. Epoxidizing a variety of non-functionalized alkenes gave yields between 20% - 52%, while functionalized alkenes (allylic alcohols) gave between 85% - 99% yield. Stereoselectivity was observed when epoxidizing aromatic alkenes and allylic alcohols using the catalysts synthesized. The results from this project suggest multiple plausible mechanisms, including a stepwise biradical pathway and Sharpless-type concerted pathway.