Preparation of Ionic Liquid Supported Organocatalysts for the Synthesis of Stereoselective (R)-9-Methyl-5(10)-Octaline-1,6-Dione

Abstract

: The synthesis of Proline-2-triethyl-ethylamide hexafluorophosphate (ILPA-PF6) (with 96% yield) and further the application during the synthesis of (R)-9-Methyl-5(10)-octaline-1,6-dione (Wieland-Miescher ketone molecule) are defined in this manuscript. The suggested protocol signifies one of the most efficient methods for the synthesis of these flexible chiral building blocks in good yield. The evident solubility of ionic liquids allows straightforward isolation of the (R)-9-Methyl- 5(10)-octaline-1,6-dione product from reaction mass. Additionally, six times catalyst recycling was considered the main conclusion of this proposed procedure. Background: The synthesis of WMK starts with the Michael Addition step, where the α, β- unsaturated ketone reacts with 2-methyl-1,3-cyclohexanedione followed by the nucleophilic attack and produces the triketone. Further, the isolated triketone goes to intramolecular Aldol Condensation, (in the Robinson Annulation reaction cascade) to get an enolate. Later, followed by the dehydrogenation reaction of enolate (to expel hydroxide ion) the desired product Wieland Miescher Ketone was isolated in good yield. The above conventional method suffers from several drawbacks like a slow reaction rate, the requirement of high boiling point solvent systems, and low reaction yield. Objective:: To prepare ionic liquid-supported organocatalysts for the synthesis of stereoselective (R)- 9-Methyl-5(10)-octaline-1,6-dione Method: This report summarizes the synthesis and its application of triethyl salt-supported prolinebased organocatalysts as recyclable and highly efficient for the asymmetric Wieland-Miescher ketone ((R)-9-Methyl-5(10)-octaline-1,6-dione). An ionic liquid-supported proline (as a catalyst) is equipped with basic proline and a significantly acidic amide moiety to promote the reaction rate, and synchronously having a specialty of ionic liquid could be easy to separate and recycle. Results:: The report simply defined the WMK molecule in good yield and enantioselectivity followed by minimal ether washing. During the reaction, low catalyst loading i.e., 0.5 g of catalyst was found enough to attain the maximum yield and enantioselectivity in 2 hours. Furthermore, catalyst recycling was observed 6 times as a significant element of the suggested catalytic method. Conclusion:: The synthesis of an extremely dynamic and enantioselective ILPA-PF6 catalytic approach is demonstrated in the report. The ILPA-PF6 catalyst was further modified after its characterization for use in the synthesis of the WMK molecule and the subsequent intramolecular aldol reaction of triketone. The WMK molecule was isolated with good yield and enantioselectivity followed by minimal ether washing. During the reaction, low catalyst loading i.e., 0.5 g of catalyst was found enough to get the maximum yield and enantioselectivity in 2 hours. Additionally, catalyst recycling was observed 6 times as a significant element of the suggested catalytic method.