Regioselective cyclization of alpha,omega-alkynoic acids catalysed by TpRu complexes: synthesis of endocyclic enol lactones [Tp = hydrotris(pyrazolyl)borate

The sigma-enynyl complex [TpRu(C(Ph)=C(Ph)C identical to CPh)(P-MeiPr2)] efficiently catalyses the regioselective cyclization of alpha,omega-alkynoic acids to yield endocyclic enol lactones having ring size up to 12 atoms.     

Multivariate optimization of the Kharasch–Sosnovsky allylic oxidation of olefins

The multivariate optimization method known as simplex is applied to the Kharasch–Sosnovsky allylic oxidation of double bonds. By applying this method, the amounts of three variables (copper source, oxidant, and additive) are optimized at the same time. Under the conditions thus obtained the reaction takes place in a considerable shorter time, being the alkene the limiting reagent. These conditions are applied to some monoterpenes and sesquiterpenes leading regioselectively to the corresponding benzoate esters, opening a route to the employment of this reaction in the synthesis of more complex molecules.     

Effects of CO<Subscript>2</Subscript> Compressibility on CO<Subscript>2</Subscript> Storage in Deep Saline Aquifers

The injection of supercritical CO₂ in deep saline aquifers leads to the formation of a CO₂ plume that tends to float above the formation brine. As pressure builds up, CO₂ properties, i.e. density and viscosity, can vary significantly. Current analytical solutions do not account for CO₂ compressibility. In this article, we investigate numerically and analytically the effect of this variability on the position of the interface between the CO₂-rich phase and the formation brine. We introduce a correction to account for CO₂ compressibility (density variations) and viscosity variations in current analytical solutions. We find that the error in the interface position caused by neglecting CO₂ compressibility is relatively small when viscous forces dominate. However, it can become significant when gravity forces dominate, which is likely to occur at late times of injection.     

11,16 Oxetane lactones. Spectroscopic evidences and conformational analysis

Sesquiterpene lactones constitute a wide group of compounds with several biological activities, including allelopathic. The naturally occurring sesquiterpene lactones dehydrocostuslactone and cynaropicrin have been modified in three different ways: preparation of 11,13-oxetane lactones, addition of a second Michael acceptor and reduction of the α-methylene-γ-lactone in order to future structure-activity relationship (SAR) studies. We have obtained all oxetane lactones stereoisomers at C-11 and C-16 positions. This fact has allowed us to establish some correlations between experimental data, derived by NMR and X-ray analysis, and the configuration at C-11 and C-16, which could be a useful tool to establish the stereochemistry as well as to confirm the presence of an oxetane ring on similar compounds. Comparative conformational analyses as a key aspect in the biological behaviour of those compounds in future structure-activity relationship (SAR) studies are presented.     

Transtaganolides A-D: novel metabolites from Thapsia transtagana

Four novel and unusual C-19 compounds from Thapsia transtagana, named transtaganolides A-D, have been isolated. Their structures were established by physical methods, including X-ray analysis of transtaganolides A and B. This is the first time that a 7-methoxy-4,5-dihydro-3H-oxepin-2-one ring has been found in a natural product. [structure: see text]     

Recent advances in the synthesis of sesquiterpenolides from Umbelliferae

A review of our latest developments in the synthesis of sesquiterpenolides isolated from plants of the Umbelliferae family is presented.     

Toward the synthesis of thapsigargin: enantioselective synthesis of 7,11-dihydroxyguaianolides

[reaction: see text] The enantioselective synthesis of a 7,11-dihydroxyguaianolide bearing the stereochemistry present in thapsigargin, a potent and selective inhibitor of the Ca(2+) SERCA-ATPase pumps, is described. Starting from (+)-dihydrocarvone, the synthesis presents two key steps. The first one involves the photochemical rearrangement of a gamma,delta-unsaturated ketone eudesmane into the corresponding guaiane. The second step consists of the regioselective oxidation of an unprotected tetrahydroxylated ketone to provide a dihydroxylactone with the required stereochemistry.     

Organotin Complexes of Alizarin and Purpurin

Five novel organotin complexes with the anthraquinone dyes alizarin (1,2‐dihydroxyanthraquinone) and purpurin (1,2,4‐trihydroxyanthraquinone) were synthesized and characterized by elemental analyses, FTIR and NMR spectroscopy (¹H, ¹³C and ¹¹⁹Sn). The crystal and molecular structures of four complexes were determined by X‐ray diffraction on single crystals: [Bu₂Sn(aliz)(H₂O)]·C₂H₅OH ( A1 ·EtOH), [Bu₂Sn(aliz)(dmso)]₂ ( A3 ), [(Bu₂Sn)₃O(Hpurp)₂] ( P1 ) and [Bu₂Sn(Hpurp)(dmso)]₂ ( P2 ), where H₂aliz = alizarin and H₃purp = purpurin. The coordination mode of the ligands is identical to that found in their Al/Ca complexes, where they act as dianionic tridentate ligands forming five and six‐membered fused chelate rings. The coordination to the tin atoms occurs exclusively via the 1,2‐ phenolate oxygen and the adjacent quinoid oxygen atoms. The complexes A1 , A3 and P1 are dimers with hepta‐coordinated tin atoms in form of a slightly distorted pentagonal bipyramid. The trinuclear complex P2 contains two pentacoordinated and one heptacoordinated tin atoms.