Transition metal and organo-catalyzed cyclizations, cycloadditions and couplings
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Transition metal-catalyzed carbon-carbon bond-forming reactions are attractive methodological targets, as they enable the rapid build-up of molecular complexity. Herein is described research directed toward the development of highly practical, efficient and selective transition metal-catalyzed processes that facilitate the succinct, sequential formation of multiple chemical bonds: i. Catalysts derived from rhodium and copper are featured in tandem conjugate addition-electrophilic trapping reactions (tandem vicinal difunctionalization), leading to products of formal aldol, Dieckmann and Blaise cyclizations. In this context, the use of diastereotopic 1,3-dione electrophilic acceptors is examined. ii. Related rhodium catalysts are employed successfully in the catalytic reductive arylation of 1,3-cyclohexadiene. iii. The classical Gilman reagent (dimethyllithium cuprate-lithium iodide) is shown to catalyze the [2+2]cycloaddition of bis(enone) substrates in high yield. Effective partitioning between the 1,4-addition and cycloaddition manifolds is showcased and discussed. Finally, a strategy for the enantioselective catalysis of photo-mediated reactions in solution is described, involving the use of chiral molecular receptors possessing appendant triplet sensitizing moieties. Energy transfer is selectively directed to bound substrate as a consequence of the distance dependence of triplet-triplet energy transfer. This effect, which is equivalent to a binding induced rate enhancement, enables substoichiometric chirality transfer from the receptor template to the substrate, as observed in the intramolecular enone-olefin photo[2+2]cycloaddition of a quinolone substrate.