Facile Ionic Liquid-Mediated, Efficient Microwave-Assisted One-Pot Green Synthesis of Privileged Linear and Angular Spirochromone Conjugates

Background: Over a decade, a number of papers have been published on the usage of ionic liquids (ILs) and Microwave-Assisted Organic Synthesis (MAOS), which displayed their benefits with respect to the conventional synthetic procedures, for current generation of fast, efficient and environmental friendly synthetic methodologies. The aim of the present study is the synthesis of linear and angular spirochromanone derivatives using microwave irradiation with the IL. As the microwave assisted organic synthesis (MAOS) with IL as a solvent is environmental friendly and non-volatile, therefore it allows simple separation and catalyst recycling. Methods: Though various methods for the synthesis of linear and angular spirochromone derivatives have been developed, one of the widely used methods is the Kabbe condensation synthesis. In this paper, we report an efficient synthesis of spirochromone conjugates by substituted 1-(6-hydroxy-3-methylbenzofuran-5-yl) ethan-1-one (1a) linear isomer or 1-(4-hydroxy-3-methylbenzofuran-5yl) ethan-1-one (1b) angular isomer with various cycloalkanones catalyzed by pyrrolidine in ionic liquid [bmim]Cl center dot AlCl3 under microwave irradiation. Results: The comparative results of 3a-g (linear isomers) and 4a-g (angular isomers) are summarized in Table 1. A series of new spirochromone conjugates synthesized were purified by column chromatography and obtained with good yields. All new compounds were synthesized and characterized by H-1 NMR, C-13 NMR, IR and LCMS. Conclusion: A new series of linear/angular spirochromanone derivatives (3a-g/4a-g) have been successfully synthesized under conventional and microwave irradiation methods using ionic liquid as solvent. The microwave irradiation with the ionic liquid mediated method has proven to be highly yielding with a higher rate of acceleration and being eco-friendly.