Selective Sonogashira Couplings in 1,2,4,5-tetrazine derivatives

1,2,4,5-Tetrazines are six-membered heterocyclic compounds in which the four nitrogen atoms are displayed in a symmetric fashion. Their reactivity is quite different from other heterocyclic aromatic systems due to its unique electron-withdrawing character, comparable to tetra-nitrobenzene. 1 In particular, 1,2,4,5- tetrazines are known to take part in [4+2] inverse-Diels–Alder cycloaddition processes which efficiently lead to the construction of substituted pyridazine systems that are important in drug development and biomarker applications. 2 However, the electronic character of 1,2,4,5-tetrazines hampered the development of 3- ethynyl- and 3,6-diethynyl-1,2,4,5-tetrazine derivatives for molecular electronic applications, proved by the scarcity of examples found in the literature. 3 Herein, we describe the synthesis and characterization of two novel ethynyl-based 1,2,4,5-tetrazine derivatives. Synthesis of 3,6-(4-bromophenyl)-1,2,4,5-tetrazine precursor (1) was achieved in good yield by Pinner’s method, starting from 4-bromobenzonitrile. Despite its low solubility in common organic solvents, this precursor was found to react smoothly under typical Sonogashira coupling conditions to selectively afford the 3-ethynyl (2) and 3,6-diethynyl (3) protected derivatives (Figure 1). Reaction conditions were evaluated in order to provide the best yields and to promote selectivity of the mono- or disubstituted ethynyl derivatives. Finally, deprotection was achieved affording, in the case of compound 3, an unprecedented 3,6- diethynyl-1,2,4,5-tetrazine compound. Time-Dependent Density Functional Theory (TDDFT) calculations for both deprotected ethynyl derivatives were used to simulate electronic spectra. A deep knowledge of the relevant electronic transitions involved and quantitatively satisfactory results of the calculated electronic excitations in comparison with experimental data were obtained.

Identidade nacional e memória colectiva em Portugal e na Alemanha: Um estudo comparativo de manuais de terceira classe

Este estudo propõe-se fazer uma análise comparativa de dois manuais de leitura do ensino primário, um em Língua Portuguesa e o outro em Língua Alemã. A pesquisa aponta afinidades e temas comuns na forma como em ambos os livros são abordados elementos representativos da identidade nacional e da memória colectiva. O nosso trabalho procura evidenciar, através dos manuais analisados e de uma fundamentação teórica, a manipulação destes conceitos durante o período do Estado Novo e do Terceiro Reich, época a que se reportam os manuais escolares. A nossa dissertação de mestrado insere-se no âmbito da Literatura Comparada, apoiando-se no que diz respeito à sua fundamentação teórica em estudos e autores trabalhados no contexto das disciplinas de Literatura e Cultura de Massas e de Literatura Infanta-Juvenil, investigações essenciais para estabelecer uma análise comparativa entre os dois manuais de leitura do ensino básico. ABSTRACT: This study aims at a comparative analysis of two primary textbooks, one in Portuguese and the other in German language. The research points out common topics, affinities as well as a similar approach to representative elements of the National Identity and the Collective Memory in Portugal and in Germany. Based on the analysis of the schoolbooks mentioned and supported by a theoretical ground basis, our work tries to show the manipulation of these concepts during the years of the Estado Novo and the Third Reich, the period of time in which both schoolbooks were published and taught. Our dissertation applies to the study field of Compared Literature, having its theoretical ground basis on studies and authors referred to in the scope of the disciplines of Literature and Culture of the Masses as well as Children’s and Youth Literature which provided us essential knowledge for a comparative analysis of these two primary schoolbooks.