Stereoselective Barbier Type Allylations and Propargylations Mediated by CpTiCl3

CpTiCl2, prepared in situ by manganese reduction of CpTiCl3, is an excellent new system for the Barbier-type allylation and propargylation of carbonyl compounds. It can be used in catalytic amounts when combined with Et3N•HBr/TMSBr, which act as regenerating system. The high regio- and stereoselectivity shown by this system makes it useful for prenylation and crotylation processes in synthesis of natural products

Ti-Catalyzed Straightforward Synthesis of Exocyclic Allenes

Exocyclic allenes constitute useful building blocks in organic synthesis and have recently been identified as key intermediates in the synthesis of natural products. Here the first general method for the most straightforward synthesis of exocyclic allenes reported to date is presented. This method is based on the Barbier-type cyclization of propargyl halides catalyzed by titanium; a safe, abundant, and ecofriendly metal. The reaction proceeds under mild conditions compatible with different functional groups and provides good yields of five-, six-, and seven-membered carbocycles and nitrogen-containing heterocycles bearing an exocyclic allene group. Experimental evidence supporting the proposed reaction mechanism is also provided. Moreover, this procedure can be carried out in an enantioselective manner by using chiral titanocene(III) catalysts. The utility of this method has been proved in the synthesis of the natural alkaloid stemoamide

Nuevas aproximaciones sintéticas hacia derivados de (+)- vernolepina a partir de germacrolidas

+ Vernolepina y + vernodalina, sustancias aisladas de las plantas etíopes Vernonia Hymenolepis y V. Amyddalina respectivamente, y el derivado sintético +8-desoxivernolepina, constiuyente un grupo de dilactonas sesquiterpénicas conesqueleto de 2-oxa-cis-decalina, que se caracterizan por presentar propiedades bilógicas intersantes. En la presente tesis doctoral, se ha estudiado una nueva estrategia para la síntesis enantioespecífica de sustancias relacionadas con + vernolepina, a partir de las germacrolidas +salonitenolida y +custunolida. El plantemaiento sintético diseñado consta básicamente de cuatro pasos claves: la transformación del esqueleto de lactona fusionado trans en un esqueleto fusionado cis; la funcionalización remota del metilo angular a partir de un hidroxilo convenientemente funcionalizado; el reordenamiento de uneposi-éster a una lactona y por último el reordenamiento de Cope del esqueletod e germacrolida a elemanolida.rsidad de Granada, Departamento de Química Orgánica. Leída el 07-04-200

Aprendizaje cooperativo y desarrollo de competencias transversales en asignaturas de la titulación de Ciencias Ambientales. Universidad de Álmería

La universidad europea y, por ende la española, se encuentra inmersa en un momento de cambio, transformación y adaptación. El nuevo paradigma hace referencia, entre otros, a la adquisición de competencias genéricas, así como a la necesidad de aprender también a través de metodologías distintas a las clásicas. En este marco, este trabajo pretende presentar el proceso, desarrollo y resultado de las experiencias de aprendizaje de tres competencias transversales en cuatro asignaturas del primer ciclo de la titulación de Ciencias Ambientales a través de técnicas colaborativas de enseñanza–aprendizaje, realizadas durante el segundo cuatrimestre del curso 2007-08.SIN FINANCIACIÓNNo data 200

Reaction of benzoxasilocines with aromatic aldehydes: Synthesis of homopterocarpans

Condensation of 2H-benzo[g][1,2]oxasilocines with aromatic aldehydes in the presence of boron trifluoride affords mixtures of cis/trans 2-phenyl-3-vinylchromans with moderate yields. These can be transformed into homopterocarpans, a synthetic group of substances homologous to the natural isoflavonoid pterocarpans

Diseño e implementación de tutoriales virtuales para el uso de fuentes de información on-line y herramientas informáticas de Química

SIN FINANCIACIÓNNo data 200

The half‐sandwich titanocene CpTi III

The half-sandwich titanocene reagent CpTiIIICl2, obtained by in situ reduction of commercial CpTiCl3 with manganese, is an excellent system for the Barbier-type reaction between aldehydes and propargylic halides, leading to homopropargylic alcohols and α-allenols. An efficient and straightforward methodology for the conversion of aldehydes into 2,5-dihydrofurans involving a two-step sequence (TiIII addition-AgI cyclization) is presented. The usefulness of the method is proved by the preparation of a Natural Product: a dihydrofuranic labdane, isolated from the leaves of Mikania sp. nov

A Concise Diastereoselective Total Synthesis of α-Ambrinol

(−)-cis-α-Ambrinol is a natural product present in ambergris, a substance of marine origin that has been highly valued by perfumers. In this paper, we present a new approach to its total synthesis. The starting material is commercially available α-ionone and the key step is an intramolecular Barbier-type cyclization induced by CpTiCl₂, an organometallic compound prepared in situ by a CpTiCl₃ reduction with Mn

A Concise Diastereoselective Total Synthesis of α-Ambrinol

(−)-cis-α-Ambrinol is a natural product present in ambergris, a substance of marine origin that has been highly valued by perfumers. In this paper, we present a new approach to its total synthesis. The starting material is commercially available α-ionone and the key step is an intramolecular Barbier-type cyclization induced by CpTiCl2, an organometallic compound prepared in situ by a CpTiCl3 reduction with Mn