The cerium(IV) ammonium nitrate (CAN)‐catalyzed sequential multicomponent reaction between tryptamine, α,β‐unsaturated aldehydes, and β‐dicarbonyl compounds affords highly substituted ...indolo2,3‐aquinolizines in a single synthetic operation. Two rings are generated through the creation of two CC and two CN bonds by a domino process comprising initial β‐enaminone formation, followed by individual Michael addition, 6‐exo‐trig cyclization, iminium formation, and Pictet–Spengler steps. Furthermore, the reaction is diastereoselective and affords exclusively compounds with a trans relationship between the H‐2 and H‐12b protons. The use of amines bearing a less nucleophilic side chain aromatic ring (5‐bromotryptamine, 3,4‐dimethoxyphenylethylamine) prevents the Pictet–Spengler final step and leads to N‐indolylethyl or N‐phenylethyl‐1,4‐dihydropyridines, which are cyclized to the corresponding indolo2,3‐aquinolizines or benzoaquinolizines in the presence of HCl in methanol/water. Treatment of the fused quinolizine derivatives with sodium triacetoxyborohydride led to the corresponding indolo2,3‐aquinolizidines or benzoaquinolizidines, possessing four stereogenic centers, as mixtures of two diastereomers.
One operation, four bonds: The cerium(IV) ammonium nitrate (CAN)‐catalyzed reaction between tryptamine, α,β‐unsaturated aldehydes, and β‐dicarbonyl compounds affords indolo2,3‐aquinolizines in a single operation (see scheme). This multicomponent reaction creates two rings by generating two CC and two CN bonds, and is proposed to take place through a domino process that involves at least five individual reactions.
A catalytic, atom-economical, domino 5-endo-dig cyclization-intramolecular olefin insertion sequence was developed under mild conditions. Aryl alkynoic acids bearing a tethered enone partner afforded ...the indeno1,2-bfuran-2-ones, the core skeleton present in a number of biologically significant molecules including the natural product solanacol, under ligand-free, palladium-catalyzed reaction conditions in high yields. The competitive β-hydride elimination in the final step leading to the conjugated analogs was avoided by the addition of lithium bromide. A plausible mechanism for this domino sequence is proposed involving intramolecular carboxypalladation and olefin insertion steps.
The cerium(IV) ammonium nitrate (CAN)‐catalyzed, three‐component reaction between primary amines, β‐dicarbonyl compounds, and α,β‐unsaturated aldehydes in ethanol heated to reflux, constitutes a ...general, one‐pot synthesis of 1,4‐dihydropyridines. Their reduction with sodium triacetoxyborohydride furnished piperidine derivatives bearing up to five substituents with full diastereoselectivity in a hitherto inaccessible stereochemical arrangement. The reaction proceeded with no significant loss of enantiomeric purity under mild reduction conditions that are compatible with several functional groups that are normally sensitive to reduction. Octahydroquinolin‐5‐one derivatives, which were prepared by a modified version of the initial multicomponent reaction, were not suitable substrates for the sodium triacetoxyborohydride mediated reduction, but they were transformed into the corresponding decahydroquinolines, including a precursor of the amphibian alkaloid pumiliotoxin C, by catalytic hydrogenation under a variety of conditions.
CAN can! The combination of a cerium(IV) ammonium nitrate (CAN)‐catalyzed, three‐component dihydropyridine synthesis with a sodium triacetoxyborohydride reduction afforded polysubstituted piperidines with complete diastereoselectivity (see scheme). The reduction step could be applied to chiral dihydropyridines without loss of stereochemical integrity. A similar strategy afforded decahydroquinolines, including a precursor to the amphibian alkaloid pumiliotoxin C.
The CAN-catalyzed three-component between reaction between primary amines, beta-dicarbonyl compounds and naphthoquinones or 2-bromonaphthoquinones afforded, respectively, 5-hydroxybenzogindoles and ...benzofindole-4,9-diones, the former of which were transformed into tetracyclic azepino1,2-abenzogindole systems through a gamma-alkylation/ring-closing metathesis sequence.
The CAN-catalyzed three-component reaction between primary amines, β-ketoesters and naphthoquinone in ethanol at room temperature afforded as the main products the corresponding Michael adducts, ...oxidized to the quinone stage. When these compounds were refluxed in ethanol in the presence of CAN, they afforded tricyclic ortho-quinones derived from the benzogindole-4,5-dione framework via a domino mechanism comprising a sequence of 5-exo-trig cyclization, elimination, Michael addition, oxo–enol tautomerism and hydroquinone oxidation individual steps.
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The cerium(IV) ammonium nitrate (CAN)-catalyzed sequential multicomponent reaction between tryptamine, alpha,beta-unsaturated aldehydes, and beta-dicarbonyl compounds affords highly substituted ...indolo2,3-aquinolizines in a single synthetic operation. Two rings are generated through the creation of two CC and two CN bonds by a domino process comprising initial beta-enaminone formation, followed by individual Michael addition, 6-exo-trig cyclization, iminium formation, and Pictet-Spengler steps. Furthermore, the reaction is diastereoselective and affords exclusively compounds with a trans relationship between the H-2 and H-12b protons. The use of amines bearing a less nucleophilic side chain aromatic ring (5-bromotryptamine, 3,4-dimethoxyphenylethylamine) prevents the Pictet-Spengler final step and leads to N-indolylethyl or N-phenylethyl-1,4-dihydropyridines, which are cyclized to the corresponding indolo2,3-aquinolizines or benzoaquinolizines in the presence of HCl in methanol/water. Treatment of the fused quinolizine derivatives with sodium triacetoxyborohydride led to the corresponding indolo2,3-aquinolizidines or benzoaquinolizidines, possessing four stereogenic centers, as mixtures of two diastereomers. PUBLICATION ABSTRACT
A simple, reproducible and efficient reverse phase high performance liquid chromatographic method has been developed for the determination of rutin in whole plant powder of Amaranthus spinosus Linn. ...The analysis was done with Waters Cosmosil C₁₈ column (150 x 4.6 mm i.d., 5 μm particle size) as stationary phase at a wavelength of 361 nm for detection and determination. The proposed HPLC method was validated for linearity, accuracy, precision and limit of quantitation.
