40002-23-1Relevant academic research and scientific papers
Modulating Reactivity and Selectivity of 2-Pyrone-Derived Bicyclic Lactones through Choice of Catalyst and Solvent
Pfennig, Toni,Chemburkar, Ashwin,Johnson, Robert L.,Ryan, Matthew J.,Rossini, Aaron J.,Neurock, Matthew,Shanks, Brent H.
, p. 2450 - 2463 (2018/03/13)
2-Pyrones, such as coumalic acid, are promising biobased molecules that through Diels-Alder reactions can provide access to a wide range of biobased chemicals, including molecules with functionality that are not easily accessible via conventional petrochemical routes. A complete reaction network and kinetic parameters for three individual diversification routes that start from a single bicyclic lactone produced via the Diels-Alder cycloaddition of coumalic acid and ethylene were examined experimentally and probed through complementary first-principle density functional theory (DFT) calculations, in situ nuclear magnetic resonance (NMR) spectroscopy, and thin film solid-state NMR spectroscopy. These experiments provide insights into the routes for several molecular structures from bicyclic lactones by leveraging Lewis or Br?nsted acid catalysts to selectively alter the reaction pathway. The bicyclic lactone bridge can be decarboxylated to access dihydrobenzenes at a substantially reduced activation barrier using γ-Al2O3 as the catalyst or selectively ring-opened via Br?nsted acids to yield 1,3-diacid six membered rings. DFT computations and microkinetic modeling in combination with experimental results provide molecular insights into the catalytically active sites on γ-Al2O3 and provide a general mechanism for the catalyzed bicyclic lactone decarboxylation in polar aprotic solvents, which involves CO2 extrusion as the kinetically relevant step. Solid-state NMR spectroscopy provides direct evidence of strong binding of the bicyclic lactone to the γ-Al2O3 surface, fully consistent with DFT simulation results and experimental reaction kinetics. In addition, the role of the solvent was examined and found to be an additional means to improve reaction rates and selectively produce alternative structures from the bicyclic intermediate. The rate of the decarboxylation reaction was increased dramatically by using water as the solvent whereas methanol acted as a nucleophile and selectively induced ring-opening, showing that both pathways are operative in the absence of catalyst. Taken together, the results demonstrate an approach for selective diversification of the coumalate platform to a range of molecules.
Regioselectivity of the Intermolecular Diels-Alder Reaction of Acyl Nitroso Compounds (C-Nitrosocarbonyl Compounds) and Nitrosoformates (O-Nitrosocarbonyl Compounds). Preparation of Functionalized cis-Δ6-1-Octalones
Boger, Dale L.,Patel, Mona,Takusagawa, Fusao
, p. 1911 - 1916 (2007/10/02)
A study of the regioselectivity of the intermolecular Diels-Alder reaction of (nitrosocarbonyl)benzene and methyl nitrosoformate with representative electron-rich and electron-deficient 2-substituted 1,3-cyclohexadienes is described.The observed results are consistent with the prediction that nitrosocarbonyl compounds behave as dependable electron-deficient 2? components in a normal (HOMOdiene controlled) Diels-Alder reaction with electron-rich 2-substituted dienes and additionally illustrate that they may serve as useful 2? components in regioselective Diels-Alder reactions with electron-deficient 2-substituted 1,3-cyclohexadienes.The latter results are consistent with either a normal (HOMOdiene controlled) or inverse electron demand (LUMOdiene controlled) Diels-Alder reaction.Utilization of the nitrosocarbonyl Diels-Alder adducts in a stereospecific preparation of functionalized, cis-Δ6-1-octalone is detailed.In contrast to predictions based on secondary orbital control (allylic axial heteroatom orbital control), cycloaddition of butadiene with the 5- and 6-substituted N-benzoyl 3-aza-2-oxobicyclooct-5-enes occurs on the face bearing the RCON-O bridge.
