University of Utah Undergraduate Research Abstracts, Volume 3, Spring 2003

Atom Efficient Preparation of Lactones From Carbon Dioxide

ATOM EFFICIENT PREPARATION OF LACTONES FROM CARBON DIOXIDE Mark Farnworth Junior Chemistry [e-mail] Faculty Sponsor: Janis Louie Dept. of Chemistry [e-mail] Participating Researchers: John E. Gibby Andrew J. Price Carbon dioxide is an attractive C1 feedstock since it is nontoxic, nonflammable, and generally inert. However, despite the extreme availability, scientists have not developed efficient ways of untapping the rich chemical nature of CO2. Limited success has been achieved with the use of transition metal 'activators'!'. Unfortunately, reaction conditions are generally harsh (high temperatures, high pressures) or require stoichiometric amounts of expensive transition metals2. Recently, we have discovered a mild and efficient method for the catalytic formation of pyrones under atmospheric pressures of CO2. Specifically, the combination of catalytic amounts of Ni(COD)2 and IPr ligand (IPr = 1,3-bis-(2,6-diiso-propylphenyl)-imidazol-2-yli-dene) mediated the [2+2+2] cycloaddition of diynes and CO2 to afford 2-pyrones. Although a variety of ligands were screened, only the sterical-ly hindered, highly electron-donating IPr ligand proved successful. Solvent, temperature, concentration, and the initial catalyst to ligand ratio were all found to be important factors that affected the yields of pyrones. A variety of diynes were subjected to the nickel-catalyzed oxidative coupling reaction which resulted in good to excellent yields of the corresponding pyrones (Table 1). From the results obtained we conclude that it is possible to create pyrones in good yields from the reaction of catalytic Ni(0) and CO2 under mild reaction conditions. The potential for utilization of such reactivity in the future is promising. We are now focusing our efforts on mechanistic understanding of this reaction. Further generalization of the reaction will also be explored. 26 (1) Takamoto, M.; Mori, M.; J. Am. Chem. Soc. 2001, 123, 2895 and references therein. (2) (a) Paddock, R.L;Nguyen/S.T.J. Am. Chem. Soc. 2001,123,11498. (b) Cheng, M.; Lobkovsky, E.B.; Coates, G. W. J. Am. Chem. Soc. 1998, 120 11018.