Nuevas Ciclaciones Catalizadas por Carbenos de Rutenio

En este trabajo de tesis se estudian detalladamente nuevas ciclaciones de derivados alquinílicos funcionalizados mediante procesos catalíticos en los cuales intervienen especies carbénicas de rutenio generadas in situ. En la primera parte de este trabajo se estudiaron las ciclaciones catalizadas por complejos de rutenio mediante procesos neutros-redox intramoleculares en alquinilacetales, éteres y carbamatos. Estos procesos requieren la generación inicial de un intermedio vinilcarbénico de rutenio electrofílico, a partir del complejo de Ru(II) inicial coordinado con diazoalcanos y alquinos, que es atrapado por un “hidruro”, un enlace Csp3-H activado por heteroátomos (O, N). En la segunda parte se estudiaron nuevas heterociclaciones de alquinales y alquinonas catalizadas por rutenio. Estas ciclaciones transcurren a través de la formación inicial de una especie vinilcarbénica de rutenio electrofílica (generada por coordinación del complejo inicial de Ru(II) con diazoalcanos y alquinos) atrapada por nucleófilos oxigenados (aldehídos y cetonas) para dar dihidropiranos, dihidro-1,4-oxazinas y epoxipirrolidinas, núcleos heterocíclicos presentes en muchos compuestos bioactivos

Vinyl Dihydropyrans and Dihydrooxazines: Cyclizations of Catalytic Ruthenium Carbenes Derived from Alkynals and Alkynones

NOTICE: This is the peer reviewed version of the following article: Cambeiro, F., López, S., Varela, J. A., Saá, C. (2014). Vinyl Dihydropyrans and Dihydrooxazines: Cyclizations of Catalytic Ruthenium Carbenes Derived from Alkynals and Alkynones. Angew. Chem. Int. Ed., 53, 23, 5959-5963. [doi: 10.1002/anie.201400675]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for self-archivingA novel synthesis of 2‐vinyldihydropyrans and dihydro‐1,4‐oxazines (morpholine derivatives) from alkynals and alkynones has been developed. The cyclizations require a mild generation of catalytic ruthenium carbenes from terminal alkynes and (trimethylsilyl)diazomethane followed by trapping with carbonyl nucleophiles. Mechanistic aspects of the new cyclizations are discussed.This work was supported by MICINN (Spain) [projects CTQ2011-28258, Consolider Ingenio 2010 (CSD2007-0006)] and Xunta de Galicia and the European Regional Development Fund (project CN2011/054 and EM 2012/051). F.C. thanks XUGA for a predoctoral contractS

Cyclization by Catalytic Ruthenium Carbene Insertion into Csp3-H Bonds

NOTICE: This is the peer reviewed version of the following article: Cambeiro, F., López, S., Varela, J. A., Saá, C. (2017). Cyclization by Catalytic Ruthenium Carbene Insertion into Csp3-H Bonds. Angew. Chem. Int. Ed. 2012, 51, 3, 723-727. [doi: 10.1002/anie.201107344]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for self-archivingA novel tandem Ru-catalyzed carbene addition to terminal alkynes/insertion of Csp3–H bonds in alkynyl acetals, ethers and amines has been accomplished under mild conditions. This cascade provides an efficient approach to form complex spiro and fused bicyclic structures in 1,5- and 1,6-hydride shift/cyclization sequences from vinylcarbene Ru intermediates.We thank the MICINN [Projects CTQ2008-06557, CTQ2011-28258, Consolider Ingenio 2010 (CSD2007-00006)] and Xunta de Galicia (2007/XA084 and CN2011/054) for financial support. F. C. thanks the Xunta de Galicia and MICINN for a predoctoral grantS

DFT and Kinetic Monte Carlo Study of TMS-Substituted Ruthenium Vinyl Carbenes: Key Intermediates for Stereoselective Cyclizations

NOTICE: This is the peer reviewed version of the following article: Cambeiro, F., Martínez-Núñez, E., Varela, J. A., Saá, C. (2015). DFT and Kinetic Monte Carlo Study of TMS-Substituted Ruthenium Vinyl Carbenes: Key Intermediates for Stereoselective Cyclizations. ACS Catalysis, 5, 11, 6255-6262. [doi: 10.1021/acscatal.5b01333]. This article may be used for non-commercial purposes in accordance with American Chemical Society Terms and Conditions for self-archivingMechanistic pathways for the cyclization of 1,5-alkynylacetal with N2CHTMS in the presence of Cp- and Cp*RuCl(cod) to afford Z and E (trimethylsilyl)vinyl spiroacetals have been calculated. Calculations show the presence of three conformers in equilibrium for the initially formed ruthenium carbenes. Differences in the stabilities and reactivities of the conformers, depending on the use of a Cp- or Cp*-ruthenium catalyst, are responsible for the favorable active reaction pathways in each case, even though the geometry of the resulting product is the same regardless of the catalyst used. Kinetic Monte Carlo (KMC) simulations with rate coefficients, including tunneling probabilities for the hydride transfer step, were used to model the evolution of reactants, intermediates and products for all calculated pathways. It was shown that one path is almost exclusively active for each catalyst. Finally, the energetic span model of Kozuch and Shaik was used to calculate the energetic span (δE), the TOF-determining transition state (TDTS), the TOF-determining intermediate (TDI) and the TOF value for each of the feasible mechanistic pathways.This work was supported by MICINN (Spain) (projects CTQ2011-28258 and CTQ2014-51912REDC), Xunta de Galicia, and the Euro-pean Regional Development Fund (projects GRC2014/032 and EM 2012/051). F.C. thanks XUGA for a predoctoral contractS

A cooperative inquiry experience for learning Science through the engagement in scientific practices

En este trabajo se describe una experiencia de indagación cooperativa encaminada a promover la participación del alumnado de secundaria en las prácticas científicas y se analizan los desempeños del alumnado relativos a la práctica de indagación. La actividad consiste en averiguar cuál sería la mejor pelota saltarina para ganar un concurso y se lleva a cabo en un aula de 4º de ESO durante tres sesiones de 50 minutos encaminadas a la preparación de la experiencia, su realización y la comunicación de los resultados. Para el análisis se examinan las producciones escritas de los estudiantes utilizando una rúbrica. Los resultados principales muestran bajos niveles de desempeño en los grupos, especialmente aquéllos relacionados con la planificación de la investigación y el establecimiento de conclusiones.This research describes a cooperative inquiry experience aimed at engaging high school students in scientific practices and analyses students' performances related to the practice of inquiry. The task consists of investigating which ball would be the best to win a bouncing contest and it is carried out in three 50-minute sessions aimed at preparing the experience (planning), its implementation and communicating the obtained results. For the analysis students’ written responses are examined by means of a rubric. The main results highlight low levels of performance, especially those related to planning the investigation and drawing conclusions

[2+1] Cycloaddition of Catalytic Ruthenium Vinyl Carbenes: A Stereoselective Controlled Access to (Z)- and (E)-Vinyl Epoxypyrrolidines

NOTICE: This is the peer reviewed version of the following article: Padín, D., Cambeiro, F., Fañanás-Mastral, M., Varela, J. A., Saá, C. (2017). [2+1] Cycloaddition of Catalytic Ruthenium Vinyl Carbenes: A Stereoselective Controlled Access to (Z)- and (E)-Vinyl Epoxypyrrolidines. ACS Catalysis, 7, 2, 992-996. [doi: 10.1021/acscatal.6b02929]. This article may be used for non-commercial purposes in accordance with American Chemical Society Terms and Conditions for self-archivingAza-alkynals undergo a cyclization reaction with diazo compounds in the presence of catalytic amounts of Cp*RuCl(cod) to afford vinyl epoxypyrrolidines, valuable building blocks for the synthesis of biologically active molecules. Ruthenium vinyl carbene intermediates have been invoked to explain the overall [2 + 1] cycloaddition (epoxy-annulation reaction). The reaction proceeds under mild conditions and in short reaction times (5–80 min) with complete (Z)- or (E)-stereoselectivity on the vinyl substituent, depending on the nature of the diazo compound used. Theoretical calculations support a mechanistic rationale to explain this controlled process.This work was supported by the Spanish MINECO (project CTQ2014-59015R), the ERDF and the Xunta de Galicia (project GRC2014/032). We also thank the ORFEO-CINQA network (CTQ2014-51912REDC). D. P. thanks MEC for a predoctoral FPU fellowship (FPU15/02132). M. F.-M. thanks MINECO for a “Ramón y Cajal” contractS

How can we assess if Limpics is a fake? Learning to plan investigations in secondary education

En este trabajo se presenta una actividad diseñada para introducir a los estudiantes de tercer curso de educación secundaria obligatoria (14-15 años) en la planificación de investigaciones en el laboratorio de química. Se utiliza un contexto relacionado con la vida cotidiana: un consorcio de empresas de productos de limpieza que lanza una campan ̃a escolar en la cual solicita colaboración a los estudiantes para desenmascarar a otra empresa rival que acaba de sacar al mercado un detergente muy eficaz llamado Limpics. Para ayudar a los estudiantes en la planificación de la investigación se les proporcionan unas tarjetas de colores con unas cuestiones. Las respuestas a dichas cuestiones, ordenadas de una forma determinada, constituirían la planificación de la investigación. Se analizan los diseños (producciones escritas) elaborados por los estudiantes (N=20) según su contenido y adecuación para resolver la investigación planteada. Los resultados principales muestran que las respuestas de los estudiantes son escuetas y poco precisas.This paper presents a task designed to introduce 9th grade students (14-15 years old) to planning investigations in the Chemistry laboratory. We used a context related to everyday life: an enterprise committee has just launched a campaign in schools in which they ask students to help them to unmask another who has announced a very efficient detergent called Limpics. To help students in planning the investigation, they were provided with coloured cards containing some questions. Their answers to these questions following a particular order will compose the planning. The analysis consists of examining students’ written designs (N=20) depending on their content and adequacy to solve the investigation. The main results point to short and little precise designs.S

Una experiencia de indagación cooperativa para aprender ciencias en educación secundaria participando en las prácticas científicas

En este trabajo se describe una experiencia de indagación cooperativa encaminada a promover la participación del alumnado de secundaria en las prácticas científicas y se analizan los desempeños del alumnado relativos a la práctica de indagación. La actividad consiste en averiguar cuál sería la mejor pelota saltarina para ganar un concurso y se lleva a cabo en un aula de 4º de ESO durante tres sesiones de 50 minutos encaminadas a la preparación de la experiencia, su realización y la comunicación de los resultados. Para el análisis se examinan las producciones escritas de los estudiantes utilizando una rúbrica. Los resultados principales muestran bajos niveles de desempeño en los grupos, especialmente aquéllos relacionados con la planificación de la investigación y el establecimiento de conclusiones