An NMR and molecular mechanics structural study on some ethereal and Δ3,10 isomers of cinchona alkaloids

Anomalous behavior of rigid cinchona alkaloids in the enantioselective hydrogenation of ethyl pyruvate in an aprotic solvent

“…(+)-DHVIN was prepared by hydrogenation of vinpocetine as described elsewhere [30]. The structure of rigid alkaloids was confirmed by 1 H NMR [31,32]. To decrease the disturbing effect of trace impurities of CN and other cinchona alkaloids both a-and b-isocinchonines were purified by preparative thin layer chromatography.…”

Effect of Microwave Irradiation on the Catalytic Activity of Palladium Supported Catalysts in the One-Step Isomerisation of Cinchona Alkaloids to Δ3,10-Isobases

“…This procedure was tested to find the optimal Literature data [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Oxidative cleavage [12][13][14][15] time for conversion of 1a or 2a to the isomers (Z/E)-3a or (Z/E)-4a. We monitored the ongoing conversion progress of substrates by taking micro-samples of the reaction mixture regularly, at 10-min intervals, which after extraction with diethyl ether in the presence of aqueous ammonia were analyzed by TLC (silica gel plates, methoxyethanol).…”

Heterogeneous Catalytic Enantioselective Hydrogenation of Activated Ketones

“…(4) shows that isocinchona alkaloids α-and β-ICN have been studied more intensively than the rest of the compounds. The reason for this is that in isocinchonas rotation is inhibited along the axis of the C8-C9 bond allowing investigation of the relationship between the conformation of the chiral modifier and ee [117,118] (Fig. (5)).…”

“…EtPy hydrogenation was therefore studied on Pt/alumina modified by isocinchona alkaloids, in AcOH and in toluene. The experimentally proven conformation of isocinchona alkaloids [117,118] has decisive importance in the successful performance of these studies. The first experimental data demonstrated the role of the open-3 conformation [107,108].…”

“…[115] and the verified structure and conformation of α-and β-ICN (Fig. (5)) [117,118] as well as on the widely accepted adsorption model [18,20], the structure of the intermediate responsible for the direction of enantioselectivity must also be different from the one universally accepted (see summaries in ref. [18,20]).…”