Fundamental insights into the enantioselectivity of hydrogenations on cinchona-modified platinum and palladium
摘要:
The influence of the configuration at the C8 and C9 positions of cinchona alkaloids was investigated by comparing the efficiency of cinchonidine, cinchonine, and 9-epi-cinchonidine as chiral modifiers. In the hydrogenation of ketones (methyl benzoylformate, ketopantolactone, methylglyoxal dimethylacetal, 2,2,2-trifluoroacetophenone) on Pt, a change in the configuration at C9 did not affect the absolute configuration of the main products; however, the ees and rates dropped significantly. In the hydrogenation of alpha-functionalized olefins (E-2-methyl-2-hexenoic acid, 2-phenylcinnamic acid, and 4-methoxy-6-methyl-2H-pyran-2-one) on Pd, replacement of cinchonidine or cinchonine by epi-cinchonidine diminished the rates and almost eliminated the enantioselection, indicating that a subtle combination of C8 and C9 configurations is required on Pd. DFT calculations of the adsorption of the modifiers and the nonlinear behavior of modifier mixtures revealed that the lower reaction rates observed for 9-epi-cinchonidine-modified surfaces cannot be related to different adsorption strength of this modifier. Additionally, substrate-modifier docking interactions are presented. (C) 2012 Elsevier Inc. All rights reserved.
Hydrogenations of triacetic acid lactone. A new synthesis of the carpenter bee ( ) sex pheromone
作者:R. Bacardit、M. Moreno-Mañas
DOI:10.1016/s0040-4039(01)85553-2
日期:1980.1
under a variety of catalytic conditions, triacetic acidlactone, I, has been hydrogenated to differently oxidized lactones (II, III and V). C-Methylation of one of them, (II) is the key step for a convenient preparation of the carpenter bee sex pheromone.
Simple and efficient synthesis of thysanone methyl ether
作者:Vivek J. Bulbule、Priti S. Koranne、Vishnu H. Deshpande、Hanumant B. Borate
DOI:10.1016/j.tet.2006.10.038
日期:2007.1
The synthesis of thysanone methyl ether is achieved by employing semivioxanthin methyl ether, which in turn is prepared by the tandem Michael addition of an anion of orsellinate to a substituted dihydropyrone.
Synthesis, Biosynthesis, and Absolute Configuration of Vioxanthin
作者:Silke E. Bode、Daniel Drochner、Michael Müller
DOI:10.1002/anie.200701014
日期:2007.8.3
Asymmetric Hydrogenation of Substituted 2-Pyrones
作者:Matthias J. Fehr、Giambattista Consiglio、Michelangelo Scalone、Rudolf Schmid
DOI:10.1021/jo982215l
日期:1999.8.1
Various substituted 2-pyrones have been hydrogenated with high enantioselectivity (up to 97% ee) to the corresponding 5,6-dihydropyrones using cationic ruthenium catalysts containing the (6,6'-dimethoxybiphenyl-2,2'diyl)bis[3,5-di(tert-butyl)phenylphosphine] ligand. When substituents at position 3 are absent, 5,6-dihydropyrones are further hydrogenated to the fully saturated delta-lactones. In the case of 4,6-dimethyl-2H-pyran-2-one, the diastereoselectivity of the second hydrogenation step was determined by the chirality of the applied catalyst, while for the 4,5,6-trimethyl-2H-pyran-2-one a double asymmetric induction effect was observed. Other cyclic substrates with endo- or exocyclic double bonds were hydrogenated, although with substantially lower enantioselectivity with respect to the 2-pyrones.
304. Unsaturated lactones. Part II. (Researches on acetylenic compounds. Part XIX.) Reactions of the esters of αβ-acetylenic hydroxy-acids with nucleophilic reagents