The homologous conjugate addition of heteroaromatic compounds to donor-acceptor cyclopropanes

The homologous conjugate addition of heteroaromatic compounds to electron deficient cyclopropanes was facilitated by calcium triflimide. The reactivity of benzofuran and 1- methylindole with a variety of differentially substituted cyclopropanes was explored and the product yields of the reactions were determined. The reaction was optimized by varying temperatures, solvents, nucleophile equivalents, calcium catalysts and co-catalysts, and catalyst loading. The optimal reaction conditions of the homologous conjugate addition were identified and yields for addition to a variety of cyclopropane substrates were obtained. Yields for the addition of benzofuran were moderate and varied from a high of 77% to a low of 28% for differentially substituted cyclopropanes. Addition of 1-methylindole proceeded in good to excellent yield, 87-99 %. The difference in yield for the two nucleophiles was significant and possible explanations for the low benzofuran yields were explored. The final products were characterized by NMR data and a potential mechanism has been proposed. The project has identified a calcium (II) complex as a robust catalyst for C–C bond for ing reactions, thus forwarding the effort to find methods that are more environmentally benign