Development of New Methodology in Organic Synthesis Enabled by Aqueous Micellar Catalysis
Green Chemistry has become a priority for conducting chemistry in both academia and industry. When advanced processes are developed in the area, chemists not only are concerned with the efficiency of the processes but also the impact on the environment. One of the major criteria of green chemistry, which is the focus of this thesis, is the replacement of organic solvents with an environmentally friendly reaction medium: water. Micellar catalysis facilitates organic reactions in water by self-assembling of surfactants, creating on organic environment for substrates and catalyst in which to perform reactions. The development of a surfactant, which serves as a solvent, is crucial for achieving syntheses under micellar catalysis conditions.
A third-generation designer surfactant, “Nok” (SPGS-550-M), commercially available from Aldrich, can be prepared in two-steps, both involving esterification using a naturally abundant plant feedstock β-sitosterol together with succinic anhydride and PEG-550-M. To evaluate this surfactant, various side-by-side transition metal-catalyzed reactions have been tested relative to TPGS-750-M (the second-generation surfactant). It has been shown that with lower cost, Nok usually affords yields that are as good as, or better than those typically obtained with TPGS-750-M.
Additionally, lowering the amount of precious metal-containing catalysts and costly ligands is preferable according to the 12 Principles of Green Chemistry and from the standpoint of economics as well. Ligand-free dehalogenation of aryl halides in water is an example of applying green chemistry principles by avoiding use of ligands and organic solvents in an important organic reaction. These mild and efficient conditions achieved via in-situ generation of dihydrogen from PdCl2/TMDS in water, subsequent dehalogenation of various functionalized aryl halides. The technology can be further expanded to include an application to multi-step synthesis, as well as showing an ability to recycle catalysts and the reaction medium.
Finally, utilizing the highly effective ligand HandaPhos for ppm gold-catalyzed reactions has been successfully performed in nanomicelles. Several cycloisomerizations of allenes have been performed giving various types of heterocyclic products in good yields. The scope of reaction also allows for intermolecular reactions such as hydration of alkynes. Although catalyst loadings are very low, this work demonstrates an ability to recycle catalysts as well as the reaction medium with consistent reactivity.