M. Mar Herrador

Weakening C−O Bonds: Ti(III), a New Reagent for Alcohol Deoxygenation and Carbonyl Coupling Olefination

Investigations detailed herein, including density functional theory (DFT) calculations, demonstrate that the formation of either alkoxy- or hydroxy-Ti(III) complexes considerably decreases the energy of activation for C-O bond homolysis. As a consequence of this observation, we described two new synthetic applications of Nugents reagent in organic chemistry. The first of these applications is an one-step methodology for deoxygenation-reduction of alcohols, including benzylic and allylic alcohols and 1,2-dihydroxy compounds. Additionally, we have also proved that Ti(III) is capable of mediating carbonyl coupling-olefination. In this sense, and despite the fact that for over 35 years it has been widely accepted that either Ti(II) or Ti(0) was the active species in the reductive process of the McMurry reaction, the mechanistic evidence presented proves the involvement of Ti(III) pinacolates in the deoxygenation step of the herein described Nugents reagent-mediated McMurry olefination. This observation sheds some light on probably one of the mechanistically more complex transformations in organic chemistry. Finally, we have also proved that both of these processes can be performed catalytically in Cp(2)TiCl(2) by using trimethylsilyl chloride (TMSCl) as the final oxygen trap.

Synthesis and antitumoral activities of marine ent-chromazonarol and related compounds

Efficient syntheses of ent-isozonarol (6a), ent-isozonarone (7a) and ent-chromazonarol (8) from (-)-sclareol (12) are described. 6a and 7a show a significative antitumoral activity.

Bioactive sesquiterpenes from Santolina rosmarinifolia subsp. Canescens. A conformational analysis of the germacrane ring

The hexane extract of aerial parts of Santolina rosmarinifolia subsp. canescens afforded eight new sesquiterpenes in addition to known compounds. Their structures were determined by spectroscopic methods and chemical transformations. The conformational analysis of the germacrane constituents was carried out by spectroscopic methods, including NMR at varying temperature and by molecular mechanics calculations. The antifeedant, antibacterial and antitumoral activity of selected compounds has been tested.

Synthesis of monoterpenic analogues of puupehenone and puupehedione

Abstract Compounds 7–8 , monoterpenic analogues of the marine metabolites puupehenone ( 1 ) and puupehedione ( 2 ), were prepared from the easily available β-cyclocitral ( 10 ) and the aryllithium derived from 11 and 12. 8 showed antitumoral activity 4–10 times higher than that for the natural products. 8 showed antitumoral activity 4–10 times higher than that of natural puupehedione.

Structural diversity from the transannular cyclizations of natural germacrone and epoxy derivatives: a theoretical-experimental study.

Treatment of germacrone (1) with different electrophiles, and of its epoxy derivatives germacrone-4,5-epoxide (2), germacrone-1,10-epoxide (3) and isogermacrone-4,5-epoxide (4) with Brönsted/Lewis acids and Ti(III), gives rise to a great structural diversity. Thus, by using a maximum of two steps, the production of more than 40 compounds corresponding to 14 skeletons is described. Computational calculations rationalizing the structural divergence produced are also described. Finally, since some of the compounds generated are bioactive natural sesquiterpenes, the mechanisms of formation of these substances will provide new insights in their biosynthesis.

Communic Acids: Occurrence, Properties and Use as Chirons for the Synthesis of Bioactive Compounds

Communic acids are diterpenes with labdane skeletons found in many plant species, mainly conifers, predominating in the genus Juniperus (fam. Cupresaceae). In this review we briefly describe their distribution and different biological activities (anti- bacterial, antitumoral, hypolipidemic, relaxing smooth muscle, etc.). This paper also includes a detailed explanation of their use as chiral building blocks for the synthesis of bioactive natural products. Among other uses, communic acids have proven useful as chirons for the synthesis of quassinoids (formal), abietane antioxidants, ambrox and other perfume fixatives, podolactone herbicides, etc., featuring shorter and more efficient processes.

New Pathways in Transannular Cyclization of Germacrone [Germacra-1(10),4,7(11)-trien-8-one]: Evidence Regarding a Concerted Mechanism

The transannular cyclization of germacrone with HSO(3)Cl at -78 degrees C by means of a concerted and regioselective mechanism gives rise to a bicyclo[6.2.0]decan-2-ylium intermediate ion, which evolves to unusual skeletons through subsequent cyclization and Wagner-Meerwein rearrangements. This novel germacra-1(10),4-diene cyclization could suggest the existence of a new biosynthetic pathway to sesquiterpenes.

The first route toward oxygenated monocarbocyclic terpenoids: synthesis of elegansidiol, a new sesquiterpene from Santolina elegans

This paper describes the isolation of elegansidiol (1), a new monocyclic sesquiterpenic alcohol, together with the known monocyclic triterpene achilleol A (2), both from Santolina elegans. The structure of 1 was confirmed by synthesis starting from 6,7-epoxygeranyl acetate (6), constituting the first route towards this type of compound.

Sesquiterpenes and phenylpropanoids fromSeseli vayredanum

Abstract 10-Hydroxy-α-humulene,10-angeloyloxy-α-humulene and 2-epilaserine have been isolated from Seseli vayredanum . The structure and stereochemistry of these new natural products were established by spectroscopic methods and chemical transformations. In addition, 12 sesquiterpene hydrocarbons, 8α-angeloyloxy-bicyclogermacrene, 3,6-epidioxy-bisabol-1,10-diene, caryophyllene oxide, 10β-acetoxy-8α-angeloyloxyslov-3-en-6,12-olide and the phenylpropanoids myristicine, eugenol methyl ether, elemicin, latifolone, laserine have also been identified.

Protecting-Group-Free Synthesis of Chokols

As a result of a combined theoretical and experimental study, we describe a two-step protocol for the preparation of an optically pure, multifunctional, cyclopentanic core shared by a number of natural products. This process is based on a hitherto unreported Ti(III)-mediated diastereoselective cyclization in which the hydroxy-directed template effect played by the Ti(III) species was found to be crucial for the stereoselective outcome of the reaction. The viability of this concept was confirmed with the first protecting-group free synthesis of three enantiopure chokols, namely, chokols K, E, and B.