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At least 289 records · Page 16Linked to original sources
PubMed2005

Enantioselective radical addition/trapping reactions with alpha,beta-disubstituted unsaturated imides. Synthesis of anti-propionate aldols.

This manuscript describes a highly diastereo- and enantioselective intermolecular radical addition/hydrogen atom transfer to alpha,beta-disubstituted enoates. Additionally, we show that anti-propionate aldol-like products can be easily prepared from alpha-methyl-beta-acyloxyenoates in good yields and high diastereo- and enantioselectivities.

Aldehydes↗
PubMed1975

The role of anionic, imidic, and amidic forms in structure-activity relationships. Correlation of electronic indices and bacteriostatic activity in sulfonamides.

The problem of structure-activity relationships in sulfonamide type compounds is tackled on the ground that both bacteriostatic activities and structural indices must be referred to the specific individual forms assumed by sulfa drugs in the active solutions. The frequency value of the symmetric stretching mode of the sulfonyl group upsilons (SO2) is chosen as a suitable electronic index and measured for the individual active forms in aqueous and Me2SO solutions. The linear correlation that exists between bacteriostatic parameter and vibration frequency (over the complete range of data at present available) proves a strict relationship between electronic structure and bacteriostatic activity in this class of drugs. Furthermore, it justifies the assumption used for the calculation of the bacteriostatic activity of the anionic form; i.e., in equilibrium with a very active species (the anion) a less active species (the neutral form) gives a negligible contribution or does not contribute at all to the total activity. The results can be summarized as follows: the lower the frequency of the symmetric stretching mode of the SO2 group of any active species of sulfonamide type compounds, the higher its bacteriostatic activity. The existence of a clear structure-activity correlation demonstrates that the whole class of compounds, whatever their form, has a single mechanism of action, while incontrovertible deviations from the general trend indicate differences or complications in the mechanism itself, but does not demonstrate that the group on which the structural index is localized plays a dominant role in the biological process. The usefulness of pKa and NH2 proton chemical shift of precursor amine as indirect indices of the electronic structure of the anionic forms is explored on extensive sets of available data.

Amides↗
PubMed2005

Ketone-imide versus ketone-oxime reductive cross-coupling promoted by samarium diiodide: new mechanistic insight gained from a failed aminocyclopentitol synthesis.

[reaction: see text] The intramolecular 1,6-ketone/imide reductive coupling promoted by samarium diiodide competes favorably with an alternative 1,5-ketone/oxime ether coupling in a keto-oxime substrate derived from D-glucosamine N-protected with a phthalimido group. This pinacol coupling reaction affords new homochiral alpha-hydroxylactam scaffolds that could be useful in diversity-oriented synthesis. A mechanistic proposal for this reaction that explains the experimental results is supported by DFT quantum-mechanical calculations on model compounds.

Cyclization↗
PubMed2006

Asymmetric Diels-Alder reactions of chiral cyclopropylidene imide dienophiles: preparation of gem-dimethyl- and spirocyclopropane norbornyl carboxylic acids.

A highly efficient strategy has been developed for the rapid asymmetric synthesis of gem-dimethyl and spirocyclopropyl norbornyl carboxylic acids. The key transformation involved the unprecedented asymmetric Diels-Alder reaction of highly reactive beta,beta-cyclopropyl-alpha,beta-unstaturated N-acyloxazolidinones with cyclopentadiene affording the adducts in high yield and de.

Carboxylic Acids↗
PubMed2002

Heterocycle annulation of enolizable vinyl quinone imides. Dihydroquinolines and quinolines from thermal 6pi-electrocyclizations and indoles from photochemical cyclizations.

[reaction: see text] Enolizable vinyl quinone mono- and diimide substrates yield protected 6-hydroxy and 6-amino dihydroquinolines by thermal electrocyclization. Aromatization provides the corresponding quinolines in quantitative yields. The quinone monoimide substrates undergo clean photochemical conversion to 5-hydroxy indoles.

Cyclization↗
PubMed2002

A mild, nonbasic synthesis of thioethers. The copper-catalyzed coupling of boronic acids with N-thio(alkyl, aryl, heteroaryl)imides.

[reaction: see text] A new synthesis of thioethers is described. The reaction of boronic acids with aryl, heteroaryl, and alkyl N-thioimides in the presence of catalytic quantities of a Cu(I) carboxylate affords good to excellent yields of thioethers. This reaction takes place in the absence of a base under mild conditions (THF, 45-50 degrees C, 2.5-12 h) and represents an interesting complement to known methods for thioether synthesis.

Boronic Acids↗
PubMed2006

Quinolactacins revisited: from lactams to imide and beyond.

Chemical analysis of a solid phase fermentation of an Australian Penicillium citrinum strain has returned all known examples of a rare class of N-methyl quinolone lactams, quinolactacins A2 (1), B2 (2), C2 (3) and A1 (4), together with the new quinolactacins B1 (5), C1 (6), D1 (7) and D2 (8), and the novel derivatives quinolonimide (9) and quinolonic acid (10). Complete stereostructures were assigned to all these compounds by detailed spectroscopic analysis and chemical interconversion. Carefully controlled and monitored decomposition studies have confirmed that quinolactacins readily undergo C-3 epimerization and oxidation, and under appropriate conditions convert to quinolonimide and quinolonic acid. Mechanisms for key transformations are proposed. The decomposition studies suggested that only quinolactacins A2 (1) and B2 (2) are genuine natural products, with all other isolated compounds being decomposition artefacts. Quinolactacins C1 (6), C2 (3), and the racemic mixture of quinolactacins D1/D2 (8/7) all displayed notable cytotoxic activity.

Imides↗