Mechanistic Studies of the Rhodium-Catalyzed Cyclization of Ortho-Formyl Styrenes

Hydroacylation is the addition of an aldehydic C-H bond across an alkene catalyzed by transition metal complexes, particularly those of rhodium, to form cyclopentanones. This reaction, which has no equivalent form in organic processes, is a facile and atom economic pathway to this type of functionalized ketone from readily available 4-pentenals. The asymmetric variant of this reaction has been extensively examined by Bosnich and others, but had not been previously applied to the asymmetric synthesis of indanones. Preliminary results from this laboratory have demonstrated that this is a highly enantioselective process, but differs in significant details from the process studied by Bosnich. In this proposal, an investigation of the mechanism of this reaction will be undertaken. The steric and electronic effects of the alkene substituent on the enantioselectivity will be examined, and some unusual kinetic observations will be explored via variation of the solvent. In addition, a newly discovered rhodium-catalyzed [4+2] cycloaddition reaction will be examined to determine the limitations of the reaction and to explore what can be learned about this mechanistically unusual reaction. This cycloaddition reaction had not been previously observed in hydro acylation reactions.

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