- Fundamental insights into the enantioselectivity of hydrogenations on cinchona-modified platinum and palladium
-
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 α-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.
- Schmidt, Erik,Bucher, Christoph,Santarossa, Gianluca,Mallat, Tamas,Gilmour, Ryan,Baiker, Alfons
-
experimental part
p. 238 - 248
(2012/06/01)
-
- Synthesis of 4-dialkylamino-and 3-halo-6-methyl-4-methoxy-2-pyranones and their 5,6-dihydro derivatives
-
A new procedure has been developed for preparation of 4-dialkylamino-6-methyl-2-pyranones and their 5,6-dihydro analogs by reaction of cyclic amines with 4-chloro- and 4-methoxy-2-pyranones. Chlorine and bromine can be introduced into position 3 of the 2-pyranone and 5,6-dihydro-2-pyranone rings via reaction of 4-methoxy derivatives with N-halosuccinimides. In the presence of two equivalents of N-halosuccinimide 3-halo-4-methoxy-6-methyl-5,6-dihydro-2-pyranone is converted into 3-halo-4-methoxy-6-methyl-2-pyranone.
- Lokot,Pashkovskii,Lakhvich
-
p. 1350 - 1354
(2007/10/03)
-
- HYDROGENATIONS OF TRIACETIC ACID LACTONE. A NEW SYNTHESIS OF THE CARPENTER BEE (Xylocopa hirsutissima) SEX PHEROMONE
-
Under a variety of catalytic conditions, triacetic acid lactone, 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.
- Bacardit, R.,Moreno-Manas, M.
-
p. 551 - 554
(2007/10/02)
-