Mild and rapid method for the generation of o-quinone methide intermediates. Synthesis of puupehedione analogues

A route to simpler analogues to bioactive puupehedione derivatives involving a hetero Diels-Alder cycloaddition of a o-quinone methide is described. These intermediate species are generated via fluoride-induced desilylation of silyl derivatives of o-hydroxybenzyl iodides. Remarkable short reaction times and very mild experimental conditions are the main features of this method.     

A convenient synthesis of a-ring-functionalized podolactones. Revision of the structure of wentilactone B

A new route to podolactones functionalized in the A ring has been achieved. Two key steps were employed in this synthesis, the construction of the bicyclic skeleton via a Mn(III)-mediated radical cyclization and the transformation of this bicyclic intermediate into the tetracyclic podolactone skeleton through a Pd (II)-mediated bislactonization of the corresponding conjugate diene. The reported synthesis of 3beta-hydroxy-13,14,15,16-tetranorlabda-7,9(11)-dien-(19,6beta),(12,17)-diolide (1) let us reassign the structure of wentilactone B, for which structure 1 was wrongly reported. [reaction: see text]     

Solid-phase selenium-catalyzed selective allylic chlorination of polyprenoids: facile syntheses of biologically active terpenoids

Regioselective halogenation of the terminal isopropylidene unit of different acyclic polyolefinic polyprenoids (farnesyl acetate, geranylgeranyl acetate, squalene, etc.) using NCS/catalytic polymer-supported selenenyl bromide is described; good to excellent yields are obtained (68-96%). The first applications of this protocol include the concise synthesis of bioactive terpenoids 1-3.     

Asteriscanolide. A sesquiterpene lactone with a new natural skeleton.

A sesquiterpene lactone was isolated from the hexane extract of $\text{Asteriscus aquaticus}$. Its constitution and stereochemistry were determined by spectroscopic techniques, principally two-dimensional NMR correlations (COSY, HCCORR, RELAY) and with the interpretation of certain chemical transformations. The results were confirmed by X-ray diffraction and the name asteriscane is proposed for the new natural skeleton.     

On the Analysis of the Mössbauer Spectra of the Rust Converted by Tannic and Phosphoric Acids

Hyperfine Interactions - In previous work, we reported results on the action of rust converters based on a mixture of tannic and phosphoric acids, upon the rust formed on mild steel coupons. There,...     

Achilleol B: a new tricyclic triterpene skeleton from Achillea odorata L

Achilleol B ( ), a new tricyclic triterpene, has been isolated from Achillea odorata L. and its structure established on the basis of its NMR data obtained through n.O.e., short and long-range homo and heteronuclear correlation experiments and other spectroscopic evidence.     

Landau Growth for Students Part I Initial Valuie Problem

This paper is internded to demonstrate to students that electron Landau growth of plasma waves is an easily understood and computed phenomenon. This derivation does not use the usual Fourier-Laplace transform technique with the inversion and final result being obtained by contour integration and residue theory. Instead, a simple treatment, following the original work of Vlasov, is used. Landau's original solution is recovered both for growth and decay, but only the growing part rigorously satisfies the initial assumptions.     

Steady cone-jet electrosprays in liquid insulator baths

This study shows that conducting liquids can be electrosprayed in steady cone-jet mode inside liquid insulator baths. Experimental results show that the current emitted from the meniscus fits well the scaling laws given in the literature for electrosprays in air at atmospheric pressure or vacuum. The technique may be of interest in obtaining fine liquid-liquid emulsions of uniformly sized droplets in the nanometric range.