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

Synthesis of chromone-related pyrazole compounds

Chromones, six-membered oxygen heterocycles, and pyrazoles, five-membered two-adjacent-nitrogen-containing heterocycles, represent two important classes of biologically active compounds. Certain derivatives of these scaffolds play an important role in medicinal chemistry and have been extensively used as versatile building blocks in organic synthesis. In this context, we will discuss the most relevant advances on the chemistry that involves both chromone and pyrazole rings. The methods reviewed include the synthesis of chromone-pyrazole dyads, synthesis of chromone-pyrazole-fused compounds, and chromones as starting materials in the synthesis of 3(5)-(2-hydroxyaryl)pyrazoles, among others. This review will cover the literature on the chromone and pyrazole dual chemistry and their outcomes in the 21st century.Thanks are due to University of Aveiro and FCT/MEC for the financial support of the QOPNA research unit (FCT UID/QUI/00062/2013) and CIQ-UP, University of Porto (POCI-01-0145-FEDER-006980; FCT: UID/QUI/00081/2013) through national founds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, as well as to the Polytechnic Institute of Bragança. V.L.M.S. is grateful to FCT for her grant (SFRH/BPD/108807/2015), in the ambit of “QREN e POCH e Tipologia 4.1 e Formação Avançada”, co-sponsored by FSE and by national funds of MCTES.info:eu-repo/semantics/publishedVersio

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

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

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

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

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

Arylxanthones and arylacridones: a synthetic overview

Arylxanthones and arylacridones although not yet found in nature are becoming an important group of heterocyclic compounds due to their promising biological activities. Their central cores, xanthone and acridone, are recognized as interesting motifs for drug development mainly to be used in antitumour chemotherapy. The synthesis of this type of compounds is still scarce but several successful examples were recently published and a large variety of arylated xanthone and acridone derivatives were prepared. A systematic survey of the literature dedicated to their synthesis will be presented and discussed in this review.Thanks are due to the University of Aveiro, Polytechnic Institute of Bragança, Fundação para a Ciência e a Tecnologia (FCT) FCT/MEC for the financial support of the QOPNA research Unit (FCT UID/QUI/00062/2013) through national founds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement. V.L.M. Silva also acknowledges FCT for the financial support of her post-doctoral grant (SFRH/BPD/108807/2015), in the ambit of “QREN e POCH e Tipologia 4.1 e Formação Avançada”, co-sponsored by FSE and by national funds of MCTESinfo:eu-repo/semantics/publishedVersio

Synthesis and transformation of halochromones

Chromones (4H-1-benzopyran-4-ones) are one of the most abundant groups of naturally occurring oxygen containing heterocyclic compounds possessing a benzo-γ-pyrone framework, 1a. The significance of these widely spread and highly diverse compounds is far beyond the important biological functions they assume in nature [1, 2]. Natural and synthetic chromone derivatives have been assigned as lead structures in drug development with some already being marketed [3]. The majority of the naturally occurring chromones are 2- and 3-aryl derivatives, called flavones 1b and isoflavones 1c, respectively. However, other types of chromones have also been found in the plant kingdom, such as 3-methylchromones 1d and 2- styrylchromones 1e (Fig. 1).University of Aveiro, Fundação para a Ciência e a Tecnologia (FCT, Portugal), European Union, QREN, FEDER and COMPETE for funding the QOPNA Research Unit

Chromones as versatile building blocks in cycloaddition reactions

4H-Chromen-4-ones commonly referred as chromones are a class of naturally occurring heterocyclic compounds implicated in a series of biological and pharmacological properties.[1] It is also an interesting scaffold involved in a range of chemical transformations for the preparation of novel and more complex oxygen-containing heterocyclic derivatives.[2] Following our interest in the chemistry of chromones, we design two different building blocks, 2- [(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones 1 and (E)-2-(4-arylbut-1-en-3-yn-1-yl)-4Hchromen- 4-ones 2, and explore the reactivity of the unsaturated systems in cycloaddition reactions. In the former case, chromones 1 were used as dienes in microwave-assisted Diels–Alder (DA) reactions with various electron-poor and electron-rich dienophiles to provide flavone-type compounds 3.[3] In the latter case, the diene system of chromones 2 was involved in DA reactions with N-methylmaleimide whereas the acetylene moiety react with sodium azide, via 1,3-dipolar cycloaddition reaction, to afford xanthene-1,2,3-triazole dyads 4.[4] In this communication, we will present and discuss the synthetic details and spectroscopic characterization of the main products and some interesting byproducts, as well as the intermediate compounds isolated in each case.Thanks are due to University of Aveiro and FCT/MEC for the financial support of the QOPNA research unit (FCT UID/QUI/00062/2013) through national founds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, and to the Portuguese NMR Network, as well as to the Instituto Politécnico de Bragança. H.M.T.A. is grateful to FCT for their PhD grant (SFRH/BD/86277/2012).info:eu-repo/semantics/publishedVersio