485-64-3Relevant articles and documents
Kinetic Studies of the Enantioselective Hydrogenation of Ethyl Pyruvate Catalyzed by a Cinchona Modified Pt/Al2O3 Catalyst
Blaser, Hans-Ulrich,Jalett, Hans-Peter,Garland, Marc,Studer, Martin,Thies, Hans,Wirth-Tijani, Amina
, p. 282 - 294 (1998)
The kinetics of the hydrogenation of ethyl pyruvate to ethyl lactate on a 5% Pt/Al2O3 catalyst in toluene was investigated both in absence and in presence of the chiral modifier 10,11-dihydrocinchonidine. It was shown that all important prerequisites for obtaining reliable kinetic data for the reaction were fulfilled. The effects on rate and enantiomeric excess of catalyst loading, modifier and substrate concentrations, hydrogen pressure, and temperature were determined for the unmodified and the modified system. The modified reaction was approximately 20-30 times faster than the unmodified reaction. A significant increase of the enantiomeric excess from 1 to 40 bar was noticed. Apparent activation energies were estimated to be 4-6 kcal/mol. Rate equations were developed for various kinetic schemes on the basis of the Langmuir-Hinshelwood-Hougen-Watson formalism and fitted to the kinetic data. Several such schemes described the measured data reasonably well and in most cases explanations other than the one considered to be the most plausible were also in agreement with our data. For the unmodified catalyst, we propose a competitive adsorption of the α-ketoester and hydrogen and the addition of the first hydrogen atom to be rate determining. On a chiral site, the rate determining step (RDS) to the major enantiomer is proposed to be the addition of the second hydrogen, whereas the RDS for the minor enantiomer remains the first H addition. On the basis of this interpretation, different proposals advanced in the literature for the mode of action of the cinchona modified Pt catalyst were compared.
Enantioselective hydrogenation of ketopantolactone
Schuerch,Schwalm,Mallat,Weber,Baiker
, p. 275 - 286 (1997)
The enantioselective hydrogenation of ketopantolactone to R-(-)-pantolactone was investigated on 5 wt% Pt/Al2O3 chirally modified with cinchonidine. The influence of catalyst pretreatment conditions, hydrogen pressure, temperature, solvent polarity, and catalyst, reactant, and modifier concentrations was studied in a slurry reactor. An enantiomeric excess (ee) of 79% at full conversion was achieved in toluene after optimization of pressure, temperature, and amount of modifier. Good ee could be obtained only after rigorous removal of traces of oxygen and water during catalyst pretreatment and from the hydrogenation reaction mixture. Molecular modeling studies (performed using molecular mechanics, semiempirical, and ab initio methods) provided a feasible structure for the diastereomeric transition complex formed between cinchonidine and ketopantolactone and an explanation for the observed enantiodifferentiation in apolar medium. The calculations indicate that formation of the complex affording R-(-)-pantolactone is energetically favored with cinchonidine, whereas the near enantiomer cinchonine favors S-pantolactone, in agreement with experimental observations. Interestingly, in apolar solvents, where the alkaloid modifier is not protonated, the modeling suggests similar structures for the diastereomeric transition complexes for the hydrogenation of ketopantolactone and methyl pyruvate.
Environmentally responsible, safe, and chemoselective catalytic hydrogenation of olefins: ppm level Pd catalysis in recyclable water at room temperature
Gallou, Fabrice,Gao, Eugene S.,Lipshutz, Bruce H.,Takale, Balaram S.,Thakore, Ruchita R.
supporting information, p. 6055 - 6061 (2020/10/14)
Textbook catalytic hydrogenations are typically presented as reactions done in organic solvents and oftentimes under varying pressures of hydrogen using specialized equipment. Catalysts new and old are all used under similar conditions that no longer reflect the times. By definition, such reactions are both environmentally irresponsible and dangerous, especially at industrial scales. We now report on a general method for chemoselective and safe hydrogenation of olefins in water using ppm loadings of palladium from commercially available, inexpensive, and recyclable Pd/C, together with hydrogen gas utilized at 1 atmosphere. A variety of alkenes is amenable to reduction, including terminal, highly substituted internal, and variously conjugated arrays. In most cases, only 500 ppm of heterogeneous Pd/C is sufficient, enabled by micellar catalysis used in recyclable water at room temperature. Comparison with several newly introduced catalysts featuring base metals illustrates the superiority of chemistry in water.
Enantioselective phase-transfer catalyzed alkylation of 1-methyl-7-methoxy-2-tetralone: An effective route to dezocine
Li, Ruipeng,Liu, Zhenren,Chen, Liang,Pan, Jing,Zhou, Weicheng
supporting information, p. 1421 - 1427 (2018/06/29)
In order to prepare asymmetrically (R)-(+)-1-(5-bromopentyl)-1-methyl-7-methoxy-2-tetralone (3a), a key intermediate of dezocine, 17 cinchona alkaloid-derived catalysts were prepared and screened for the enantioselective alkylation of 1-methyl-7- methoxy-2-tetralone with 1, 5-dibromopentane, and the best catalyst (C7) was identified. In addition, optimizations of the alkylation were carried out so that the process became practical and effective.
Indium-mediated catalytic enantioselective allylation of N -benzoylhydrazones using a protonated chiral amine
Kim, Sung Jun,Jang, Doo Ok
supporting information; experimental part, p. 12168 - 12169 (2010/10/03)
A catalytic enantioselective indium-mediated allylation of N-benzoylhydrazones in conjunction with a protonated chiral amine affording enantioenriched homoallylic amines with an extremely high level of enantioselectivity and chemical yield was developed.
