Chalcones, a Privileged Scaffold: Highly Versatile Molecules in [4+2] Cycloadditions

Este documento es una revisión sobre el uso de las chalcones como bloques de construcción en la síntesis de moléculas complejas, vía una cicloadición [4+2] de Diels-AlderChalcones are aromatic ketones found in nature as the central core of many biological compounds. They have a wide range of biological activity and are biogenetic precursors of other important molecules such as flavonoids. Their pharmacological relevance makes them a privileged scaffold, advantageous for seeking alternative therapies in medicinal chemistry. Due to their structural diversity and ease of synthesis, they are often employed as building blocks for chemical transformations. Chalcones have a carbonyl conjugated system with two electrophilic centers that are commonly used for nucleophilic additions, as described in numerous articles. They can also participate in Diels-Alder reactions, which are [4+2] cycloadditions between a diene and a dienophile. This microreview presents a chronological survey of studies on chalcones as dienes and dienophiles in Diels-Alder cycloadditions. Although these reactions occur in nature, isolation of chalcones from plants yields very small quantities. Contrarily, synthesis leads to large quantities at a low cost. Hence, novel methodologies have been developed for [4+2] cycloadditions, with chalcones serving as a 2π or 4π electron system.Secretaría de Investigación y Estudios Avanzados de la UAEMex. CONACYT PRODEP DAIP, Universidad de Guanajuat

Synthesis of Diarylamines and Methylcarbazoles and Formal Total Synthesis of Alkaloids Ellipticine and Olivacine

En este documento se describe la síntesis química, vía microondas, de derivados de alcaloides elipticina y olivacina, así como su identificación espectroscópica inequívocas.New and efficient strategies for the conversion of 4-oxazolin-2-ones into 1-methyl and 1,4-dimethyl 3-formylcarbazoles are herein described. Highly convergent cascade and one-pot processes afforded the corresponding diarylamines, as in situ formed synthetic intermediates or final products in high overall yields. Special attention was given to the synthesis of methylated carbazoles by reacting 4,5-dimethyl-4-oxazolin-2-ones with enones under microwave irradiation. The carbazole scaffold was provided by the palladium(II)-catalyzed double C−H activation to generate oxidative cyclization of diarylamines. This methodology allowed for formal total syntheses of four naturally occurring pyrido[4,3-b]carbazole alkaloids ellipticine, 9-methoxyellipticine, olivacine, and 9-methoxyolivacine.Secretaría de Investigación y Estudios Avanzados de la UAEMex. CONACYT Ludwig K. Hellweg Foundation Secretaría de Investigación y Posgrado, del IP

A novel and chemoselective process of N-alkylation of aromatic nitrogen compounds using quaternary ammonium salts as starting material

Artículo Internacional Open AccesThe process of N-alkylation of several pyrroles, indoles, and derivative heterocycles is herein described, using quaternary ammonium salts as the source of an alkylating agent. These reactions were carried out on several heterocyclic rings with triethylbenzylammonium chloride or tetradecyltrimethyl ammonium bromide and an NaOH solution at 50%, leading to a chemoselective N-alkylated product and an average yield of 73%. This is an alternative process to the traditional benzylation and methylation of N-heterocycles with direct handling of alkyl halides.CONACYT, Secretaría de Investigación y Estudios Avanzados de la UAE

Antifungal activity of 10-homo-N-1,2,3-triazol-bicyclic carbonucleosides: A novel type of compound afforded by azide-enolate (3+2) cycloaddition

The first report of 1′-homo-N-1,2,3-triazol-bicyclic carbonucleosides (7a and 7b) is described herein. Azide-enolate (3+2) cycloaddition afforded the synthesis of this novel type of compound. Antifungal activity was evaluated in vitro against four filamentous fungi (Aspergillus fumigatus, Trichosporon cutaneum, Rhizopus oryzae and Mucor hiemalis) as well as nine species of Candida spp. as yeast specimens. These pre-clinical studies suggest that compounds 7a and 7b are promising candidates for complementary biological studies due to their good activity against Candida spp.Secretaria de Investigación y Estudios Avanzados (SIEA) de la Universidad autónoma del Estado de México (UAEMex