Sintese de derivados 3 - substituídos de coumarinas

Este trabalho descreve a síntese de novos derivados de coumarinas 3-substituídas por grupos arilo, etenilarilo e etenil-organometálicos, através de novas metodologias via reacções de Heck e de metátese (Grubbs), com controlo da regioquímica e com significativos rendimentos reaccionais. A aplicação destas metodologias permitiu a síntese dos derivados, 3-fenilcoumarina (131), 3-(4-bromofenil)coumarina, (132), 3-(4-iodofenil)­coumarina (134), 3-(4-nitrofenil)coumarina (136), 3-(4-etilfenil)coumarina (133), 4-(coumarin-3-il)benzaldeído (135), 3-(4-metoxifenil)coumarina (137), (E)-3-acrilato-[4-(coumarin-3-il)fenil] de metilo (138), 6,7-metileno­dioxi-[3-(E)-2'-feniletenil]coumarina (145), 6,7-dimetoxi-[-(E)-2'-fenil­etenil]coumarina (146), 6,7-dimetoxi-[3-(E)-2'-(6'-nitrofenil)etenil]coumarina (147), 4-[2-(E)-(6,7-dimetoxicoumarin-3-il)etenil]benzaldeído (148) e 6,7-dimetoxi-[3-(E)-2'-ferroceniletenil]coumarina (149), dos quais os últimos nove, são compostos novos, identificados e caracterizados pela primeira vez. A deslocalização do sistema de electrões  conjugados, induzida pelos diversos substituintes das coumarinas, foi igualmente avaliada através da espectroscopia de UV/Vis. De referir que parte deste trabalho foi publicado como: "New Methodology for the Synthesis of 3-Substituted Coumarins via Pd-Catalyzed Site-Se/ective Cross-Coupling Reactions”, Sérgio Martins, Paula S. Branco, María C. de la Torre, Miguel A. Sierra e António Pereira, Synlett, 2010 (https://www.thieme-connect.com/ejournals/abstract/ synlett/doi/1 O.1 OS5/s-0030-1259014). ABSTRACT: This work describes the synthesis of new 3-aryl, ethenylaryl and ethenyl-organometallics coumarin derivatives, using a new methodology via Heck and metathesis (Grubbs) reactions, with regiochemistry control and significant reaction yields. The application of these methodologies allowed the synthesis of derivatives, 3-phenylcoumarin (131), 3-(4-bromophenyl)coumarin (132), 3-(4-iodophenyl)coumarin (134), 3-(4-nitrophenyl)coumarin (136), 3-(4-ethylphenyl)coumarin {133), 4-(coumarin-3-yl)benzaldehyde {135), 3-(4-methoxiphenyl)coumarin (137), (E)-ethyl 3-[4(coumarin-3-yl)phenyl]­acrylate (138), 6,7-methylenedioxy-[3-(E)-2'-phenylethenyl]coumarin (145), 6,7-dimethoxy-[-(E)-2'-phenylethenyl]coumarin (146), 6,7-dimethoxy-[3-(E)­-2'-(6'-nitrophenyl)ethenyl]coumarin (147), 4-[2-(E)-(6,7-dimethoxy­coumarin-3-yl)ethenyl]benzaldehyde {148) e 6,7-dimethoxy-[3-(E)-2'-(ferro­ cene)ethenyl]coumarin (149), the last nine of these are new compounds, identified and characterized for the first time. The delocalization of conjugated -electron system, induced by different substituents of coumarins, was also assessed by spectroscopy UV/Vis. Part of this work was published at: "New Methodology for the Synthesis of 3-Substituted Coumarins via Pd-Catalyzed Site-Selective Cross-Coupling Reactions", Sérgio Martins, Paula S. Branco, María C. de la Torre, Miguel A. Sierra e António Pereira, Synlett, 2010 (https://www.thieme­connect.com/ejournaIs/abstract/synlett/doi/1O.1 055/s-0030-1259014).

Tracing acidification induced by Deccan Phase 2 volcanism

The Deccan Volcanic Province (DVP) was built up by three major phases of eruptions; the most voluminous of which, the Deccan Phase 2, encompassed the Cretaceous–Palaeogene (KT) boundary. Deccan eruptions have been implicated as a contributor to the end-Cretaceous mass extinction, however, mechanism by which volcanic activity affected biota remains poorly understood. We applied a combination of rock magnetic techniques scanning electron microscopy to characterize mineral assemblages of three sections of intertrappean lacustrine sediments from the north-western Maharashtra Deccan Volcanic Provinces. Our results indicate that in sediments deposited during the early stages of the Deccan Phase 2, the Daïwal River and Dhapewada sequences, iron-bearing mineral association is dominated by detrital iron oxides (magnetite and hematite) sourced from the weathering of the surrounding basaltic bedrocks, with minor contribution form authigenic iron sulphides (framboidal pyrite, pyrrhotite and/or greigite). The sediments deposited during the final stages of Phase 2 (the Podgawan sequence) differ significantly in their characteristics. In particular, the Podgawan sediments have 1) very low magnetic susceptibility values, but higher terrigenous fraction (clays and shales) content; 2) more complex assemblage of magnetic minerals, 3) ubiquitous presence of Fe–Ca–Ce vanadates; and 4) unusual lithological variations in the middle part of the section (represented by a charcoal-rich level that is capped by a red clay layer containing fossilized bacterial colonies). We suggest that these unusual characteristics reflect increased acidity in the region during the deposition of the Podgawan sequence, likely due to cumulative effects of volcanic aerosols released during the Deccan Phase 2 eruptions. The combination of these features may be used to recognize episodes of increased acidity in the geological record. Our results also contribute to understanding of local vs. global effects of the Deccan volcanism.