Visible light induced C-C bond formation

This Ph.D thesis demonstrates the development of new methodologies for C-C bond formation triggered by visible light photoredox catalysis. In Chapter 1, we have outlined a short overview on Copper in Photocatalysis. Starting from the photophysical properties of copper complexes, a comparison of main excited state aspects of prevalently used ruthenium and iridium complexes with that of copper has been shown. Several UV and visible light mediated synthetic transformation utilizing copper catalysts has been described. In Chapter 2, aim of this work has been described. In Chapter 3, allylation of α-halo carbonyl compounds has been described employing allyl tributyltin and [Cu(dap)2Cl] as visible light photoredox catalyst. Utilizing a very low catalyst loading, mono allylation of α-halo ketones and di-allylation of α, α-dibromo and α, α-dichloroketoneshas has been achieved. In Chapter 4, we describe the atom transfer radical addition (ATRA) of electron deficient benzyl halides to styrenes and silyl enol ethers utilizing [Cu(dap)2Cl] as photocatalyst. To further emphasize on the utility of this methodology, products derived from ATRA of 2-nitrobenzyl bromide to different styrenes successfully converted to biologically important tetrahydroquinolines. In Chapter 5, a visible light phototoredox catalyzed methodology for vinyl radical generation from α-bromochalcone and cinnamates utilizing an iridium based photocatalyst has been described. The vinyl radicals were efficiently engaged in cascade cyclization with different heteroarenes like furan, benzofuran, pyrrole and indole for the synthesis of novel polycyclic frameworks in excellent yields. A single electron transfer from photocatalyst to substrate has been proposed. Presence of vinyl radical in reaction medium was corroborated by additional experiments. In Chapter 6, we have described a vinyl radical annulation sequence to olefins for the synthesis of 3,4-dihydronaphthalenes. A wide range of terminal alkenes with different functional groups were efficiently converted to dihydronaphthalenes. A plausible reaction mechanism based on oxidative quenching of photocatalyst was proposed. Radical trapping experiments with TEMPO supported the vinyl radical mechanism. To demonstrate further the application of the methodology, some of the dihydronaphthalenes were efficiently converted to naphthalenes. In Chapter 7, we have described an efficient method for the α-vinylation of ketones. Vinyl radicals, generated by an iridium catalyst from α-bromochalcones under visible light irradiation, were coupled with enol acetates to furnish 1,4-diketones. Aromatic, aliphatic and alicyclic enol acetates were suitable partners for this coupling reaction. A reaction mechanism is proposed involving a photo induced electron transfer from the excited photocatalyst to α-bromochalcones forming vinyl radicals