1,721,041 research outputs found
TiCl4-promoted addition of nucleophiles to open chain alpha-amidoalkylphenyl sulfones
No full textLinear a-amidoalkylphenyl sulfones are converted into the corresponding N-acyliminium ions by treatment with TiCl4 at
low temperature and then made to react with different nucleophiles such as allyltrimethylsilane, silyl ketene acetal, anisole and thiophene
Aza-Henry reaction of substituted nitroalkanes using alpha-formamidoaryl sulfones as N-acylimino equivalents
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Synthesis of (Z) -9,10-Epoxynonacosane, a Long-Chain Epoxide Isolated from Stem Was of Rubus thibetanus
No full textNew cyclopeptide alkaloids from Ziziphus mucronata
No full textZiziphus mucronata (rhamnaceae), known in South Africa as the "buffalo thorn", is reported to have numerous magico-medicinal uses. Pharmacological investigations have shown sedative, analgesic, anti-inflammatory and antibacterial activities.
The alkaloid extract of the roots afforded as main component the already known cyclopeptide alkaloid mucronine-D.
Among the minor compounds O-demethyl mucronine-D, and a new cyclopeptide alkaloid, which is an isomer of sativanine-K, were isolated.
The structure of the three compounds have been mainly determined through recent 1D- (selective excitation) and 2D-NMR (long-range C-H correlation and ROESY)
Recent Advances in Stereoselective Syntheses Using N-Acylimines
No full textAbstract: The electron-withdrawing aptitude displayed by the acyl group makes N-acylamines very attractive substrates in many processes aimed at the preparation of amino derivatives. The remarkable electrophilicity of N-acylimines can be profitably used to overcome reactivity troubles often observed using N-alkylimines and N-arylimines. The presence of a polar acyl moiety on the nitrogen atom is particularly effective in stereoselective reactions were electrostatic interactions play a major role in determining the facial preference for the nucleophilic attack. Utilization of alkoxycarbonyl groups (e.g. Boc or Cbz) as activating N-acyl substituents allows one to obtain the final amino derivative in a protected form that can be readily cleaved under mild conditions. In this review, several synthetic applications of N-acylimines in stereoselective reactions that have appeared in the literature since 1990 are discussed.
1 Introduction
2 Preparation of N-Acylimines
3 Nucleophilic Additions to N-Acylimines
3.1 Reaction with Organometallic Reagents and Related Carbanions
3.1.1 Linear N-Acylimines
3.1.2 Cyclic N-Acylimines
3.2 Reaction with Enolate Anions
3.2.1 Nitroalkanes: The Aza-Henry Reaction
3.2.2 1,3-Dicarbonyls
3.2.3 Carbonyls and Related Derivatives
3.2.4 Carboxylic Acid Derivatives
3.3 Reaction with Aromatic Compounds
3.4 Reaction with Heteronucleophiles
4 Cycloaddition Reactions
5 Conclusio
Taxanes from the roots of Taxus x media cv Hicksii
No full textThe plants of genus taxus commonly known as yew tree have been used since the ancient times for their magic, poisonous and pharmacological properties.
Studies devoted to chemical constitution of extracts of several Taxus genera have been extensively developed during the last years, according to the well documented anticancer activity of taxol.
The bark of several yew species has been thoroughly investigated, but very few studies have been done on the constituents of roots. The roots of an ornamental variety of yew (T. x media cv Hicksii) gave a series of taxane and abeotaxane pseudoalkaloids. Both N-alkylated O (5) esters (taxines) and N-acylated O (13) esters (Taxols) were isolated, some of them in glycosidic form. Besides known compounds, some new taxines, taxols and abeotaxanes were isolated and their structures fully elucidated
A mild,efficient and selective method for desilylation of more common trialkyl ethers by Cerium ( III ) chloride heptahydrate and sodium iodide in acetonitrile
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