Enantioselective Michael addition of isobutyraldehyde to nitroalkenes organocatalyzed by chiral primary amine-guanidines

Primary amine-guanidines derived from trans-cyclohexane-1,2-diamines are used as organocatalysts for the enantioselective conjugate addition of isobutyraldehyde to arylated and heteroarylated nitroalkenes. The reaction was performed in the presence of imidazole as the additive in aqueous DMF as the solvent at 0 °C. The corresponding Michael adducts bearing a new stereocenter were obtained in high yields and with enantioselectivities of up to 80%. Theoretical calculations are used to justify the observed sense of the stereoinduction.

Enantioselective Michael addition of aldehydes to maleimides organocatalysed by chiral 1,2-diamines: an experimental and theoretical study

Simple and commercially available chiral 1,2-diamines were used as organocatalysts for the enantioselective conjugate addition of aldehydes, including α,α-disubstituted, to maleimides. The reaction was carried out in the presence of hexanedioic acid as an additive in aqueous solvents at room temperature. By employing (1S,2S)- and (1R,2R)-cyclohexane-1,2-diamine as organocatalysts, the corresponding Michael adducts bearing new stereocenters were obtained in high or quantitative yields with enantioselectivities of up to 92%, whereas the use of (1S,2S)-1,2-diphenylethane-1,2-diamine gave a much lower ee. Theoretical calculations were used to justify the observed sense of the stereoinduction.

Enantioselective Synthesis of Succinimides by Michael Addition of Aldehydes to Maleimides Organocatalyzed by Chiral Primary Amine-Guanidines

The monoguanylation of (1S,2S)- and (1R,2R)-cyclohexane-1,2-diamine affords chiral primary amine-guanidines that are used as chiral organocatalysts in the enantioselective Michael addition of aldehydes, particularly α,α-disubstituted aldehydes, to maleimides. The reaction is carried out in the presence of imidazole, as an additive, in aqueous N,N-dimethylformamide, as the solvent, and affords the corresponding enantioenriched succinimides in high or quantitative yields with enantioselectivities up to 96 % ee. Theoretical calculations (DFT and M06–2X) suggest a different hydrogen-bonding coordination pattern between the maleimide (C=O) and the catalyst (NH groups) is responsible for the enantioinduction switch that is observed when the reaction is carried out using primary amine-guanidines versus primary amine-thioureas as the organocatalysts.

Enantioselective Synthesis of Succinimides by Michael Addition of 1,3-Dicarbonyl Compounds to Maleimides Catalyzed by a Chiral Bis(2-aminobenzimidazole) Organocatalyst

A wide variety of chiral succinimides have been prepared in high yields and enantioselectivities by asymmetric conjugate addition of 1,3-dicarbonyl compounds to maleimides under very mild reaction conditions using a bifunctional benzimidazole-derived organocatalyst. Computational and NMR studies support the hydrogen-bonding activation role of the catalyst and the origin of the stereoselectivity of the process.

No tan diferentes. La actividad empresarial de los siderúrgicos españoles en el contexto europeo (1891-1936)

A la hora de explicar las causas del atraso relativo de España en las décadas previas a la Guerra Civil, algunos autores han considerado como un factor clave la mayor propensión de los empresarios españoles a las estrategias de búsqueda de rentas, lo que dio lugar a un sector industrial protegido, cartelizado e ineficiente. Dado que la siderurgia es señalada frecuentemente como el paradigma de las funciones improductivas de los empresarios españoles, el presente trabajo pretende, en primer lugar, contrastar las actitudes de los siderúrgicos españoles con las de los franceses y alemanes en las décadas que precedieron a la Primera Guerra Mundial. En segundo lugar, se analizará si la cartelización del mercado entre 1897 y 1936 tuvo consecuencias negativas para el desarrollo económico de España, tales como restricción a la entrada de competidores, ausencia de innovaciones tecnológicas y, como resultado de ello, una oferta rígida para su producción.

Solvent-dependent enantioswitching in the Michael addition of α,α-disubstituted aldehydes to maleimides organocatalyzed by mono-N-Boc-protected cyclohexa-1,2-diamines

Enantiomerically pure mono-N-Boc-protected trans-cyclohexa-1,2-diamines are used as organocatalysts for the enantioselective conjugate addition of α,α-disubstituted aldehydes to maleimides. Using a single enantiomer of the organocatalyst, both enantiomeric forms of the resulting Michael adducts bearing a new quaternary stereocenter are obtained in high yields, by only changing the reaction solvent from chloroform (up to 86% ee) to aqueous DMF (up to 84% ee).

Un médico rural contra la viruela, la epidemia de 1891-92 en Huércanos (Logroño)

La práctica inconstante de la vacunación contra la viruela durante el siglo xix tuvo como consecuencia la aparición de varias oleadas epidémicas en España. La baja aceptación de la vacuna entre la población, unida a la incapacidad del estado para organizar campañas y suministrar vacuna, contribuyeron a perpetuar la enfermedad. Durante la segunda mitad del siglo se abrió un debate sobre la necesidad de hacer obligatoria la vacunación y revacunación, incorporándose, además, el uso de la vacuna animalizada. Un texto de Emilio Casas Arriola, médico de Huércanos (Logroño), describe el brote epidémico sufrido entre 1891 y 1892 en este municipio. La obra tiene la estructura de una topografía médica y fue redactada con la intención de concurrir a un premio de la Real Academia Médica de Madrid. Se analizan las dificultades, vicisitudes y medidas adoptadas para afrontar la epidemia en un entorno aislado y rural.