Abstract:
Organocatalysis has become one of the essential pillars of asymmetric catalysis, complementing enzyme and chiral metal catalysis. Over the last few decades, various carbon-carbon and carbon-hetero (C-C and C-X) bond-forming reactions such as the aldol reaction, Diels-Alder reaction, Mannich reaction, Friedel-Craft reaction, Morita-Baylis-Hillman (MBH) reaction, Stetter reaction, etc. have been explored under organocatalytic condition. Among these, the Morita-Baylis-Hillman (MBH) reaction has become one of the most important, popular, and versatile methods for constructing C-C, C-X bonds. The dense functionalities and versatile reactivity of Morita-Baylis-Hillman (MBH) adducts make them powerful precursors for building various carbocyclic, heterocyclic, and biologically important compounds. In recent years, pyrazolonone-derived MBH carbonates have emerged as a versatile synthon for constructing multi-functional spiropyrazolonone scaffolds under organocatalytic conditions.
We have been working in the field of organocatalysis over the years. We have effectively utilized the Morita-Baylis-Hillman carbonates of pyrazolonone and 3-Methylene Oxindole to construct different spiroheterocycles. Diastereoselective bis-spiropyrazolonone and spirooxindole have been successfully synthesized under tertiary amine catalysis. These spiroheterocycles have been synthesized via (3+2) cycloaddition pathway. Later, we explored the photoreactivity of 3-methylene oxindole under visible light irradiation to construct highly diastereoselective 3-4 fused spirooxindoles in one pot. Interestingly, this light-driven diasterioselective (4+2) cyclization occurs at an unusual unactivated C4 position (of 3-methylene Oxindole) without requiring any pre-functionalization. Further, we have successfully demonstrated the base catalyzed diastereoselective synthesis of tetraazadispiro pyrazolone framework via oxa-Michael cascade (4 + 2) annulation in a rapid reaction time (2 mins). Further, we extended the scope of base catalysed transformation for the diastereoselective synthesis of spiropyrazolone fused pyrolidines in rapid time (5-20 min).
