Organocatalysts, small organic molecules that catalyze reactions, have been employed with incteasing frequency. MacMillan's amine catalysts have been used in the synthesis of eunicillin, a secondary metabolite present in soft corals. Eunicillin is a structurally novel diterpene that features a rare oxacyclic ring system, and the synthesis of these medium sized ringed oxacycles have been previously difficult. Holmes and coworkers were able to synthesize this molecule through an intermolecular organocatalyzed Diels-Alder reaction, which featured a cis fused hexahydroisobenzofuran moiety flanked by a characteristic nine membered ring . The (S) catalyst was found to be efficient in producing the desired stereoselectivity, but the origins of the differences between the (R)- and (S)- MacMillan catalysts remain unclear.We report a detailed theoretical study of the intramolecular Diels-Alder reaction used in the synthesis of the tricyclic core of �unicillin in order to elucidate the origins of stereoselectivity.We have also studied the thermal and catalyzed reactions of acyclic analogs and simple model systems, as well as 7-membered, and 8-membered analogs of the 9-membered precursor to the core of Eunicellin.

Origins of stereoselectivities in intramolecular Diels-Alder cycloadditions catalyzed by chiral imidazolidinones, and their application to the synthesis of eunicillin

245th National Meeting (2013)

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