Synthetic Attempts with Visible Light Catalysis and Metal Catalysis Towards Dearomatization and Related Intrigues

Abstract

Chapter-I: Photo-redox Catalytic Radical Relay for para-Selective Amination and Aminative Dearomatization of Phenols and Anilines An efficient organic photocatalytic para-selective amination and aminative dearomatization of phenols and anilines with azodicarboxylates is developed. The formation of para-amino pheno or aniline and para- amino cyclohexadinone depends on whether it has a para- substitution or not. Organic photocatalyst riboflavin tetraacetate (RFTA) is successfully demonstrated to avoid metal contamination. The reaction condition is simple and mild, giving high selectivity with good to excellent yield. A broad substrate scope and nice functional group tolerance, with scalability and post functionalization, make the protocol worthy. Chapter-II: Photocatalytic ortho-Selective Amination and Aminative Dearomatization of Phenols and Naphthols via Synergistic use of Phase Transfer Catalysis in Water An organo-photocatalytic ortho-selective amination and aminative dearomatization of phenols and naphthols is developed using azodicarboxylates as aminating reagent. The key achievement of this protocol is the use of phase transfer catalysts (PTC) such as ammonium bromide salts, which not only made the reaction medium completely aqueous but also induced ortho-selectivity. The formation of ortho-amino phenol or naphthol and ortho-amino cyclohexadinone depends on whether it has an ortho-substitution or not. The reaction condition is simple and mild, giving high regioselectivity with moderate to good yield. A broad range of substrate variation with good functional group tolerance and the application of the protocol for scale-up reactions along with post functionalization make the protocol worthy. Chapter-III: Access to z-Enynoate Equipped Coumarin Employing Organic Photocatalysis A photocatalytic protocol for the synthesis of 3-ester-4-alkynyl (z-enynoate) coumarin is reported using eosin Y as a suitable organic photocatalyst. The protocol was executed under mild conditions like room temperature, organic photocatalysis, less reaction time, and visible light irradiadtion. The exemplary functional group tolerance and concerted activation of the dual mode of catalyst eosin Y make this protocol useful. Again, the product formed bears the scope for broad synthetic applications such as the hydrogenation gave 3,4- dihydro coumarin, an important motif in organic synthesis. Chapter-IV: Ruthenium (VIII) Catalyzed Dearomative Pyridyl C-X Activation: Direct Synthesis of N- Alkyl-2- pyridinones An efficient synthetic strategy employing pyridyl C-X activation for the generation of N-alkyl- 2-pyridinones from N-alkyl-2-halopyridinium salts is described. As pyridinones are dearomatized synthetic derivatives of pyridines, a versatile scope exists for pyridyl C-H functionalization. The present strategy exemplifies a straightforward in situ generation of Ru(VIII), leading catalytic dearomative synthesis of pyridinones. The N-alkyl-2-pyridinones, are further reduced to N-alkyl-2-piperidinones and a plausible mechanism is also drawn, supported by some controlled reactions. Chapter-V: Trials Towards Photocatalyst Free Visible Light Catalyzed Synthesis of [3]Cumulene-1-ol via Encouraged Boron-Catalysis The synthesis of tetra-substituted [3]cumulene-1-ol via photocatalysis with boron co-catalysis has been reported. The beauty of this protocol is the use of simple and normal conditions like room temperature, metal and catalyst free, visible light as activation source and molecular oxygen as oxidant. The post-modification of the obtained [3]cumulene-1-ol resulted in an important organic precursor, allenic ketone.