Thomas Werner

Phosphorus-based Bifunctional Organocatalysts for the Addition of Carbon Dioxide and Epoxides

Bifunctional phosphonium salts were synthesized and employed as organocatalysts for the atom efficient synthesis of cyclic carbonates from CO2 and epoxides for the first time. These catalysts were obtained in high yields by a modular, straightforward one-step synthesis. The hydrogen-bond donating alcohol function in the side chain leads to a synergistic effect accelerating the catalytic reaction. The desired cyclic carbonates are obtained in high yields and selectivity under solvent-free reaction conditions without the use of any co-catalyst. Under optimized reaction conditions various epoxides were converted to the corresponding cyclic carbonates in excellent yields. The products were obtained analytically pure after simple filtration over a silica gel pad. This protocol is even applicable for a multigram reaction scale. Moreover, the catalysts could be easily recovered and reused up to five times.

Bifunctional One‐Component Catalysts for the Addition of Carbon Dioxide to Epoxides

Several bifunctional ammonium salts were synthesized and employed as one‐component catalysts for the conversion of CO2 and epoxides to produce cyclic carbonates. These catalysts show superior activities compared to their monofunctional analogs. A turnover number of up to 693 and a turnover frequency of up 392 h−1 could be achieved for the best catalyst. Moreover, the effect of various solvents has been studied. All employed solvents and the product formed had a negative influence on substrate conversion. The scope and limitation of the reaction has been studied carefully for two general reaction protocols at 45 and 90 °C. In over 20 examples, the isolated yields after filtration were 90 %. In addition, we present the first organocatalyzed synthesis of a cyclohexene‐based naturally occurring cyclic carbonate, and its molecular structure was determined by XRD. Furthermore, we demonstrate that the reaction can be performed even on a multigram scale and can be monitored by in situ FTIR spectroscopy.

Hydroxyl‐Functionalized Imidazoles: Highly Active Additives for the Potassium Iodide‐Catalyzed Synthesis of 1,3‐Dioxolan‐2‐one Derivatives from Epoxides and Carbon Dioxide

4(5)‐(Hydroxymethyl)imidazole and potassium iodide were identified as an efficient catalyst system for the cycloaddition of epoxides and carbon dioxide producing 1,3‐dioxolan‐2‐one derivatives under solvent‐free conditions. The high activity of the catalyst system even at 60 °C was probably due to synergistic effects between potassium iodide and the substituted imidazole. Various functionalized and nonfunctionalized terminal epoxides as well as internal epoxides were converted into the corresponding cyclic carbonates in high yields (up to 99 %) under mild reaction conditions within a short reaction time. Compared with the previously reported amino alcohols e.g. triethanolamine based catalyzed synthesis of cyclic carbonates, the catalyst system described herein demonstrates a higher activity toward a broad substrate scope

First Base-Free Catalytic Wittig Reaction

The first base-free catalytic Wittig reaction utilizing readily available Bu3P (5 mol %) as an organocatalyst is reported. The initial Michael addition of the phosphine to a suitable acceptor substituted alkene ultimately results in the formation of an ylide which is subsequently converted with an aldehyde. The presented (1)H NMR studies actually reveal evidence for the Michael addition and proposed ylide formation. Under the optimized reaction conditions various maleates and fumarates were converted with aromatic, heteroaromatic, and aliphatic aldehydes to evaluate the scope and limitations of this unprecedented reaction. Notably, maleates and fumarates react in a stereoconvergent fashion. The corresponding products were obtained in up to 95% isolated yield and E/Z-selectivities up to 99:1.

B(C6F5)3-Catalyzed Michael Reactions: Aromatic C–H as Nucleophiles

The Michael reaction is a widely used reaction for the C-C coupling of electron-poor olefins and C(sp3)-H pronucleophiles. Herein we report the Michael reaction between alkenes and aromatic as well as heteroaromatic compounds as aromatic C(sp2)-H nucleophiles under mild conditions. The reaction is catalyzed by readily available Lewis acidic B(C6F5)3 and proceeds with high regioselectivity for a wide substrate scope.

B(C6F5)3-Catalyzed Regioselective Deuteration of Electron-Rich Aromatic and Heteroaromatic Compounds

Deuterium labeled compounds find widespread application in life science. Herein, the deuteration of electron-rich (hetero)aromatic compounds employing B(C6F5)3 as the catalyst and D2O as the deuterium source is reported. This protocol is highly efficient, simply manipulated, and successfully applied in the deuteration of 23 substrates including natural neurotransmitter-like melatonin. It is assumed that the weakening of the O-D bond ultimately results in the formation of electrophilic D+.

Copolymerization of CO2 and epoxides mediated by zinc organyls

Herein we report the copolymerization of CHO with CO2 in the presence of various zinc compounds R2Zn (R = Et, Bu, iPr, Cy and Ph). Several zinc organyls proved to be efficient catalysts for this reaction in the absence of water and co-catalyst. Notably, readily available Bu2Zn reached a TON up to 269 and an initial TOF up to 91 h−1. The effect of various parameters on the reaction outcome has been investigated. Poly(ether)carbonates with molecular weights up to 79.3 kg mol−1 and a CO2 content of up to 97% were obtained. Under standard reaction conditions (100 °C, 2.0 MPa, 16 h) the influence of commonly employed co-catalysts such as PPNCl and TBAB has been investigated in the presence of Et2Zn (0.5 mol%). The reaction of other epoxides (e.g. propylene and styrene oxide) under these conditions led to no significant conversion or to the formation of the respective cyclic carbonate as the main product.

Crystal structure of diethyl (E)-2-[(benzo-furan-2-yl)methyl-idene]succinate.

The title compound, C17H18O5, was synthesized by a base-free catalytic Wittig reaction. The molecule consists of a diethyl itaconate unit, which is connected via the C=C double bond to a benzofuran moiety. The benzofuran ring system (r.m.s. deviation = 0.007 Å) forms dihedral angles of 79.58 (4) and 12.12 (10)° with the mean planes through the cis and trans ethoxycarbonyl groups, respectively. An intramolecular C—H⋯O hydrogen bond involving the O atom of the benzofuran moiety is observed. In the crystal, molecules are linked into ribbons running parallel to the b axis by C—H⋯O hydrogen bonds.

2-Hy­droxy­ethyl­ammonium iodide

In the crystal structure of the title salt, C2H8NO+·I−, N—H⋯O, N—H⋯I and O—H⋯I hydrogen bonds lead to the formation of layers staggered along the c axis.