Six-membered ring systems: with O and/or S atoms

The most interesting chemistry published in 2020 on the synthesis of O- and S-six-membered heterocycles is reviewed. This personal overview is focused on the developments made on the synthesis of a large variety of natural compounds, specific reactions, and reagents for the preparation of natural and synthetic pyrans, chromenes and chromans, isochromenes and isochromans, pyranones, coumarins and isocoumarins, chromones and chromanones, xanthenes and xanthones, thiopyrans and analogues, dioxanes, dithiins, and also oxathianes.info:eu-repo/semantics/publishedVersio

A 31P nuclear magnetic resonance study of phosphate levels in roots of ectomycorrhizal and nonmycorrhizal plants of Castanea sativa Mill.

31P-Nuclear Magnetic Resonance (NMR) was used to assess phosphate distribution in ectomycorrhizal and nonmycorrhizal roots of Castanea sativa Mill. as well as in the mycorrhizal fungus Pisolithus tinctorius in order to gain insight into phosphate trafficking in these systems. The fungus P. tinctorius accumulated high levels of polyphosphates during the rapid phase of growth. Mycorrhizal and nonmycorrhizal roots accumulate orthophosphate. Only mycorrhizal roots presented polyphosphates. The content in polyphosphates increased along the 3 months of mycorrhiza formation. In mycorrhizal roots of plants cultured under axenic conditions, the orthophosphate pool decreased along the culture time. In nonmycorrhizal roots the decrease in the orthophosphate content was less pronounced. The level of orthophosphate in mycorrhizal roots was significantly lower than in nonmycorrhizal ones, which indicates that this system relies upon the fungal polyphosphates as a major source of phosphate

A Multiple Criteria Framework to Evaluate Bank Branch Potential Attractiveness

Remarkable progress has occurred over the years in the performance evaluation of bank branches. Even though financial measures are usually considered the most important in assessing branch viability, we posit that insufficient attention has been given to other factors that affect the branches’ potential profitability and attractiveness. Based on the integrated used of cognitive maps and MCDA techniques, we propose a framework that adds value to the way that potential attractiveness criteria to assess bank branches are selected and to the way that the trade-offs between those criteria are obtained. This framework is the result of a process involving several directors from the five largest banks operating in Portugal, and follows a constructivist approach. Our findings suggest that the use of cognitive maps systematically identifies previously omitted criteria that may assess potential attractiveness. The use of MCDA techniques may clarify and add transparency to the way trade-offs are dealt with. Advantages and disadvantages of the proposed framework are also discussed.

Epoxidação de (E,E)-Cinamilidenoacetofenonas com Peróxido de Hidrogénio

As (E,E)-cinamilidenoacetofenonas pertencem a um importante grupo de cetonas a,β,Y,∂-insaturadas, cuja síntese envolve a condensação aldólica de acetofenonas com cinamaldeídos adequadamente substituídos. Certos derivados saturados, as 1,5-diaril-1-pentanonas, foram isolados a partir de plantas usadas na medicina tradicional da Africa tropical, da Ásia e da Austrália e demonstraram possuir forte actividade anti-bacteriana.2 No entanto, os compostos desta família com mais aplicações são as (E,E)-2'-hidroxicinamilidenoacetofenonas, as quais constituem uma importante classe de intermediários na síntese de 2- estirilcromonas.3 A epoxidação deste tipo de compostos com dimetildioxirano ou com o método de epoxidação assimétrica de Juliá já foi descrita, embora neste último caso se tenha utilizado um só derivado.4 Tendo em conta o nosso estudo da reactividade de (E,E)- cinamilidenoacetofenonas e a potencialidade dos epóxidos obtidos na síntese duma grande variedade de novos compostos, decidiu-se estudar o efeito da utilização do catalisador de salen Mn(III) na epoxidação da (E,E)-cinamilidenoacetofenona 1a usando o H2O2 como oxidante

Novel Hydroxy-9H-xanthen-9-ones derivatives: synthesis and bioactive properties

9H-Xanthen-9-ones commonly referred as xanthones are a large group of natural heterocyclic compounds with significant bioactive properties (e.g. anti-inflammatory, antibacterial, antimalarial, cytotoxicity and radical scavenging activity).1 In order to explore some of these biological assessments, we developed two methodologies for the synthesis of novel hydroxylated 2,3-diarylxanthone derivatives. The first synthetic route is based on the Heck reaction of the 3-bromochromone 2 followed by aldol condensation and electrocyclisation/oxidation processes to afford the 2,3-diaryl-9H-xanthen-9-ones 1. An efficient and more general approach is the Heck reaction of 3-bromo-2-styrylchromones 3 with styrenes as olefins followed by the in situ electrocyclisation/oxidation processes.2 Pharmacological studies involving the hydroxy-9H-xanthen-9-ones 1,3 which are obtained after cleavage of the methyl group, will also be presented and discussed

Synthesis of new hydroxy-2-styrylchromones

http://apps.isiknowledge.com/full_record.do?product=UA&search_mode=GeneralSearch&qid=5&SID=V1M67gPH3IpI7j5a98j&page=1&doc=1&colname=WOSHydroxy-2-styrylchromones 5a−i were prepared by debenzylation of benzyloxy-2-styrylchromones 3a−i, which were synthesised by the Baker−Venkataraman method. The last step of this method, the cyclodehydration 5-aryl-3-hydroxy- 1-(2-hydroxyaryl)-2,4-pentadien-1-ones 2a−i, was carried out with a catalytic amount of iodine, or p-toluenesulfonic acid, in DMSO. Benzyloxy-3-cinnamoyl-2-styrylchromones 4a−f were obtained as by-products in both procedures, but the latter procedure gave benzyloxy-2- styrylchromones 3a−i in better yields. The structures of all new compounds were established by extensive NMR studies

Explicit group USSOR method for solving elliptic partial differential equations

This paper presents a new 4-points Explicit Group Unsymmetric Successive Overrelaxation (USSOR) iterative method to approximate the solution of the linear systems derived from the discretisation of self-adjoint elliptic partial equations. Several studies have been carried out by many researchers on the USSOR iterative method, for example, the analysis of its convergence [1], an upper bound for its error [2] and recently a special case of the USSOR, namely the SSOR method has been used to approximate the solution of augmented systems [4] and [8]. The computational behaviour of this new method and a comparison with its point version is presented

Stationary micropolar fluid with boundary data in L2

AbstractWe consider the Dirichlet boundary value problem for the equations of a stationary micropolar fluid in a bounded three-dimensional domain. We show the existence and uniqueness of a distributional solution with boundary values in L2

NMR in the epoxidation of (E,E)-Cinnamylideneacetophenones

The epoxidation of cinnamylideneacetophenones have been already performed with hydrogen peroxide as an oxidant in Julia's method [1] and with dimethyldioxirane [2], however no studies were performed using salen Mn(III) complexes as catalysts.The epoxidation of cinnatnylideneacetophenones have been already performed with hydrogen peroxide as oxidant in Julia's method [1] and with dimethyldioxirane [2], however no studies were performed using salen Mn(lll) complexes as catalysts. On these basis, we developed a study on the epoxidation of cinnamylideneacetophenones 1, catalyzed by coinmercially available Jacobsen's catalyst [salen Mn(IIl)] and using iodosy I benzene and hydrogen peroxide as oxidants. The structure of the epoxidation products 2-5, their stereochemistry and the regiochemistry of the monoepoxides 2 fotmation were established by ID and 2D NMR spectroscopy. These studies will be presented and discussed

Cholesterol-based compounds: Recent advances in synthesis and applications

This review reports on the latest developments (since 2014) in the chemistry of cholesterol and its applications in different research fields. These applications range from drug delivery or bioimaging applications to cholesterol-based liquid crystals and gelators. A brief overview of the most recent synthetic procedures to obtain new cholesterol derivatives is also provided, as well as the latest anticancer, antimicrobial, and antioxidant new cholesterol-based derivatives. This review discusses not only the synthetic details of the preparation of new cholesterol derivatives or conjugates, but also gives a short summary concerning the specific application of such compoundsThanks are due to the University of Aveiro, Instituto Politécnico de Bragança, FCT/MEC for financial support of the QOPNA (FCT UID/QUI/00062/2013) and CIMO (UID/AGR/00690/2013) research units, through national funds, and where applicable cofinanced by the FEDER, within the PT2020 Partnership Agreement; and also to the Portuguese NMR Network. This work was also supported by the Integrated Programme of SR&TD “pAGE–Protein aggregation Across the Lifespan” (reference CENTRO-01-0145-FEDER-000003), co-funded by the Centro 2020 program, Portugal 2020, European Union, through the European Regional Development Fund. H. M. T. Albuquerque thanks the pAGE project for his Post-Doc grant (BPD/UI98/4861/2017).info:eu-repo/semantics/publishedVersio