Transition Metal-Catalyzed Cycloaddition Reactions for the Formation of Eight- and Six-Membered Rings

Throughout this dissertation, the versatility of metal-catalyzed cycloaddition reactions for synthesizing structurally diverse bicyclic systems has been demonstrated. Nickel-catalyzed intramolecular [4+4]-cycloadditions have led to cis-eight-membered fused [6.3.0] and trans- or cis- eight-membered fused [6.4.0] bicyclic systems. These intramolecular [4+4]-cycloadditions proceeded efficiently on a set of bis-dienes linked by a three- or four-atom chain to afford cis- or trans-configured bicyclic systems, with one cyclic motif being an eight-membered ring. Computational studies on the stereo-determining step of the reaction have helped rationalize the stereochemical outcome of the reaction. The mechanistic insights gained within the present work for nickel-catalyzed intramolecular [4+4]-cycloadditions contributed to developing an enantioselective version of this transformation with a thorough screening of enantiopure phosphorus- and nitrogen-containing ligands. Research activities within the present dissertation have also demonstrated the versatility and efficacy of XBPhos-Rh combined with silver BArF as catalysts for intramolecular [4+2] cycloadditions of dienynes. This cycloaddition reaction proceeded efficiently on a set of structurally diverse dienynes to afford six-membered carbocycles fused to a five-membered ring. The products were isolated as 1,4-unconjugated cyclohexenes, without aromatization taking place. A tentative rationalization of the reaction pathway involving a Rh/Ag cooperative mechanism has also been suggested.

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