Green Techniques to Improve Grignard Reactions and Synthesize Heterocyclic Molecules

Green chemistry integrates environmentally safe and sustainable technologies for chemical research and production. Many classical synthetic methods, even with widespread applicability and significance, have various drawbacks due to the use of harsh conditions, harmful reagents, long reaction times and the generation of large amounts of waste. The goal of this thesis is to apply some of the twelve principles of green chemistry to modify traditional processes or develop new processes for chemical synthesis. The majority of organometallic reagents are supplied in solvents lacking greenness from an environmental and process safety perspective. This research was carried out focusing on the solvent influence in a series of the Grignard reactions to encourage suppliers to provide the Grignard reagents in a greener solvent. The study showed 2-methyltetrahydrofuran, which can be derived from renewable resources, was superior or equal to typical ethereal solvents used. It was also demonstrated that judicious selection of the initiator and use of hybrid solvent systems such as MeTHF-CPME/toluene broadened the scope of potential solvents to be employed in Grignard reactions. The reactions were systematically evaluated based on reaction efficiency, ease of work-up, and safety. In a separate study, new efficient method was developed to synthesize substituted furans which are known to exhibit various biological activities. Herein, the tetrasubstituted furans were prepared by a three-step synthesis including condensation of a fluorous benzaldehyde followed by Michael-type [3 + 2] cycloaddition and Pd-catalyzed coupling reactions such as Suzuki and Buchwald amination for fluorous linker cleavage. The combination of a microwave reaction and fluorous solid-phase extraction (F-SPE) was used to improve reaction and separation efficiency. Multi-component reactions aid in the rapid construction of complex molecules by incorporating all the reactants at once. An atom- and step-efficient synthesis of biaryl substituted furocoumarin, furoquinolone, and furopyrimidine derivatives was established. The bromobenzaldehydes act as key bi-functional molecules to conduct the multi-component and Suzuki coupling reactions in sequence. The ether linkage to form carbon-oxygen bond was obtained by a Pd-catalyzed coupling reaction of flourous sulfonates. Diverse scaffolds were achieved by using fast microwave reactions of various alcohols with a variety of flourous molecules. Additionally, several complex compounds were also synthesized for biological screening and quantitative structure activity relationship (QSAR) studies