Ralf Jackstell

Selective Catalytic Hydrogenation of Diethyl Oxalate and Related Esters

The reduction of esters into alcohols is an important basic transformation in organic chemistry. On the laboratory scale, as well as for the synthesis of fine chemicals, these reactions are typically performed with stoichiometric amounts of metalhydride reagents, such as LiAlH4 or NaBH4. Clearly, catalytic hydrogenation reactions constitute a more economic and “greener” approach, in which only the respective alcohol is produced as a by-product and salt waste is avoided. Whereas heterogeneous hydrogenation catalysts, which are often applied in industry, work under harsh conditions (>200 8C, 200 bar), defined organometallic catalysts can be used at lower temperatures. Furthermore, the use of tailormade ligands for specific substrates can allow control over the chemoand regioselectivity of a reaction. Hence, the interest in homogeneous catalysts in this area has increased in recent years and several systems for the homogeneous hydrogenation of esters, acids, amides, and nitriles have been reported. Notable recent improvements in the hydrogenation of carboxylic acid esters have been reported by the groups of Milstein, Saudan, Saito, and others. Based on our interest in the hydrogenation of nitriles and esters, we started to investigate the hydrogenation of oxalic acid esters, in which their general reduction into the corresponding glycolates and ethylene glycol, as well as unwanted dehydration reactions, were possible (Scheme 1).

Efficient and selective Palladium‐catalyzed Telomerization of 1,3‐Butadiene with Carbon Dioxide

A more efficient telomerization of 1,3‐butadiene with carbon dioxide leading to the valuable δ‐lactone 1 (3‐ethylidene‐6‐vinyltetrahydro‐2H‐pyran‐2‐one) is reported. The key to success is the use of a palladium/TOMPP‐catalyst system (TOMPP=tris‐(o‐methoxyphenyl)‐phosphine), which provided under optimal conditions significantly increased yields of the desired product and improved catalyst turnover numbers (TON=1500).

Recent Progress in Carbon Dioxide Reduction Using Homogeneous Catalysts

Efficient chemical transformations of carbon dioxide into value-added chemicals are of growing importance in academic and industrial laboratories. In this respect, the reduction of carbon dioxide to formic acid, methanol etc., offers interesting possibilities. Herein, we describe the recent developments in carbon dioxide reductions mainly focusing on the use of defined organometallic catalysts and in some cases organocatalysts are also included.

Efficient and selective palladium-catalyzed telomerization of 1,3-butadiene with carbon dioxide

Statement of the Problem: Catalytic synthesis of organic sulfenamides and disulfides has great significance and value in synthetic chemistry and bioscience. Despite the prominent applications of sulfenamides, there are only a few reports about their preparation. In this contribution, we reported an oxidative coupling of 2-mercaptobenzothiazole leading to 2,2-disbenzothiazoledisulfide in up to 94 % yield.G acid (GABA) is a precursor to pyrrolidone, a monomer used for the production of a biodegradable polymer known as nylon-4. GABA is also widely used in the medical industry to treat conditions such as high blood pressure, anxiety and depression. Generally, GABA is produced from glutamate by the enzyme glutamate decarboxylase (GadB). In this study, a synthetic scaffold complex was introduced between Pyrococcus horikoshii GadB and the GABA antiporter (GadC) from E. coli. P. horikoshii GadB was attached to the N-terminus, C-terminus and middle of E. coli GadC via scaffolding. Among the three scaffold complexes evaluated, the N-terminus scaffold model produced 5.93 g/L of GABA from 10 g/L monosodium glutamate (MSG). When the gabT mutant E. coli XBT strain was used, the highest GABA concentration of 5.96 g/L was obtained, which is 97.8% of GABA yield. In addition to GABA concentration, GABA productivity was increased 3.5 fold via the synthetic scaffold complex.