Epoxidation O 0218Oxidation of Alkenes by Oxodiperoxomolybdem: Trialkyl (aryl)phosphine Oxide Complexes. -The epoxidation of alkenes with stoichiometric or catalytic amounts of the title complexes in the presence of tBuOOH or hydrogen peroxide is investigated. Some positive results are presented in the scheme. -(ALTINIS KIRAZ, C. I.; MORA, L.; JIMENEZ*, L. S.; Synthesis 2007, 1, 92-96; Dep. Chem. Chem. Biol., Rutgers State Univ. N. J., Piscataway, NJ 08854, USA; Eng.) -Mais 19-031
Catalytic amounts of short-chain (2-4 carbons) trialkylphosphine oxide ligands and MoO 5 have been shown to efficiently convert di-and higher substituted alkenes to the corresponding epoxides using a biphasic system with either 30% hydrogen peroxide or 70% TBHP acting as the stoichiometric oxidant.Epoxides provide useful intermediates in the synthesis of various natural products and organic materials. Both in homogeneous and heterogeneous catalysis, complexes of many transition metals including Ti, W, Ru, V, Re, Mn, Cr, Rh, and Mo have been utilized in delivering oxygen to alkenes. 1 Moreover, diperoxo complexes of group 5, 2 group 6, 3 and group 7 4 elements have been the focus of recent research for potential industrial use as oxidants.We recently reported the synthesis of a series of oxodiperoxomolybdenum·trialkylphosphine oxide (Mimountype) 5 complexes which oxidize indoles to a variety of products depending on the substitution pattern at carbons 2 and 3. 6 We report here both the stoichiometric and catalytic epoxidation of several representative alkenes with the oxodiperoxomolybdenum·trialkyl(aryl)phosphine oxide complexes 1-5.A stoichiometric reaction was performed with cyclooctene to identify the most active complex in the epoxidation of this alkene. The reactions were performed at room temperature in anhydrous dichloromethane under an atmosphere of nitrogen and with equimolar amounts of cyclooctene and oxidant (Table 1). Isolated yields were moderate due to the volatility of cyclooctene oxide, but conversion of the alkene to epoxide as measured by integration of the NMR peaks of the starting substrate and product 7 were high to essentially complete.The results indicate that complex 2 is the most active oxidant as conversion to the epoxide is achieved within 40 minutes. Conversely, oxidant 1 utilizing trimethylphosphine oxide as ligand required 48 hours to form cyclooctene oxide due to low solubility of this complex in organic solvents. The rest of the coordinatively saturated complexes formed the epoxide exclusively; no over-oxidation to ketones or epoxide opening to form diols was observed with any of the complexes.Once the most active oxidants were identified, stoichiometric oxidations were performed on other alkenes to further elucidate the activity of these complexes ( Table 2). Oxidations of terpenes such as a-pinene led to formation of rearranged products; several aldehyde peaks were visible by 1 H NMR spectroscopy. It is well known that complete transformation of terminal alkenes lacking electrondonating substituents to epoxides is difficult. 8 Not surprisingly, when terminal alkenes were subjected to stoichiometric oxidation conditions with 2 or 3 only 40-60% conversions were observed over several days. Results of a Density Functional Theory (DFT) study on factors that effect reactivity in epoxidations with Mimoun complexes indicates that the activation barrier to epoxidation can be significantly reduced with incorporation of electron-donating substituents on the alkene double bond. 9In stoichiome...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.