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

A large variety of publications involving O- and S-6-membered ring systems have appeared in 2017. The importance of these heterocyclic compounds is highlighted by the huge number of publications on the total synthesis of natural oxygen derivatives and of other communications dedicated to synthetic derivatives. Reviews on stereoselective organocatalytic synthesis of tetrahydropyrans (17EJO4666), of tetrahydropyrans and their application in total synthesis of natural products (17CSR1661), on the synthesis of the less thermodynamically stable 2,6-trans-tetrahydropyrans (17S4899), on enantioselective synthesis of polyfunctionalized pyran and chromene derivatives (17TA1462), and on enantioselective and racemic total synthesis of camptothecins, including the formation of their pyran-2-one ring (17SL1134), have appeared. Advances in the transition metal-catalyzed synthesis of pyran-2/4-ones (17TL263), N-heterocyclic carbene (NHC)-catalyzed achiral synthesis of pyran-2-one, coumarin and (thio)chromone derivatives (17OBC4731), on the synthesis and transformation of 2H-pyran-2-ones (17T2529) and 2-styrylchromones (17EJO3115) into other heterocyclic compounds, have been surveyed. The strategies to build up the tetrahydropyranyl core of brevisamide (17H(95)81) and the reactions of ketyl radicals, generated from carbonyl derivatives under transition-metal photoredox-catalyzed conditions, leading to isochromen- and chroman-type compounds (17CC13093) were disclosed. Developments in the synthesis of pentafluorosulfanyl(chromene and coumarin) derivatives (17TL4803), photoswitchable D9-tetrahydrocannabinol derivatives (17JA18206), and aminobenzopyranoxanthenes with nitrogen-containing rings (17JOC13626) have been studied.info:eu-repo/semantics/publishedVersio

Distribution of Naturally Occurring Anthraquinones, Iridoids and Flavonoids from Morinda genus: Chemistry and Biological activity

The present review covers chemistry and bioactivities of anthraquinones, iridoids, and flavonoids from the Morinda genus. The plants of Morinda species, belonging to the Rubiaceae family, have been used as traditional folk medicine with anti-bacterial, anti-fungal, anti-tumor, anti-helmin, analgesic, anti-inflammatory, and immune enhancing effects. They are rich sources of anthraquinones and iridoids. The relevant 2-methoxy-1,3,6-trihydroxyanthraquinone is one of the most potent quinone reductase enzyme inducers with no cytotoxicity with normal cells. Damnacanthol-3-O-b-D-primeveroside and lucidin-3-O-b-D-primeveroside displayed a significant reduction of the blood glucose levels in anti-diabetic tests. Additionally, iridoids, 9-epi-6a-methoxy geniposidic acid, scandoside methyl ester, asperulosidic acid, showed a more potent inhibitory effect of melanogenesis than the commercial available depigmented arbutin used in cosmetic industry

(1R,3R,4R,6S)-4-(7-Methoxy-2-oxo-2H-chromen-6-yl)-1-methyl-3,6-dioxabicyclo[3.1.0]hexan-2-yl acetate

In the title compound, C17H16O7, which was isolated from the leaves of Micromelum integerrimum, the furan ring adopts an envelope conformation with the O atom as the flap. An intramolecular C—H...O hydrogen bond occurs. The carbonyl O atom is disordered in a 0.57 (8):0.43 (8) ratio. In the crystal, molecules are linked by weak C—H...O hydrogen bonds into a C(10) chain along [010]

Approach to the Synthesis of 2,3-Disubstituted‑3<i>H</i>‑quinazolin-4-ones Mediated by Ph₃P–I₂

Readily available <i>N</i>-substituted amides or their requisite carboxylic acids or acid chlorides have been used to construct 2,3-disubstituted-3<i>H</i>-quinazolin-4-ones in a one-pot procedure. Key transformation in this convergent approach involves Ph₃P–I₂-mediated formation of amidine upon condensation of an amide or the intermediate amide with methyl anthranilate. Cyclization of the amidine-tethered anthranilate then affords 2,3-disubstituted-3<i>H</i>-quinazolin-4-ones in good to excellent yields under mild conditions

Ph₃P/I₂‑Mediated Synthesis of <i>N,N</i>′<i>,N</i>″‑Substituted Guanidines and 2‑Iminoimidazolin-4-ones from Aryl Isothiocyanates

A convenient one-pot procedure for the synthesis of acyclic and cyclic guanidines mediated by the Ph₃P/I₂ system is described. Sequential condensation of aryl isothiocyanates with amines followed by dehydrosulfurization and guanylation could lead to both symmetric and unsymmetric <i>N,N</i>′<i>,N</i>″-substituted derivatives. Through a tandem guanylation–cyclization, a series of 2-iminoimidazolin-4-ones could also be prepared in good yields from the reaction of aryl isothiocyanates with amino acid methyl esters

Application of <i>N</i>‑Acylbenzotriazoles in the Synthesis of 5‑Substituted 2‑Ethoxy-1,3,4-oxadiazoles as Building Blocks toward 3,5-Disubstituted 1,3,4-Oxadiazol-2(3<i>H</i>)‑ones

5-Substituted-2-ethoxy-1,3,4-oxadiazoles were conveniently prepared through a one-pot sequential <i>N</i>-acylation/dehydrative cyclization between ethyl carbazate and <i>N</i>-acylbenzotriazoles in the presence of Ph₃P–I₂ as a dehydrating agent. Subsequent treatment with a stoichiometric amount of alkyl halides (X = Cl, Br, I) enables a rapid access to a variety of 3,5-disubstituted 1,3,4-oxadiazol-2­(3<i>H</i>)-ones in good to excellent yields

Ultrasound-Assisted Solvent-Free Parallel Synthesis of 3‑Arylcoumarins Using <i>N</i>‑Acylbenzotriazoles

An ultrasound-assisted one-pot acylation/cyclization reaction between <i>N</i>-acylbenzotriazoles and 2-hydroxybenzaldehydes has been developed for the synthesis of substituted 3-arylcoumarins. Using ultrasound not only allows rapid and clean conversion but also simplifies experimental setup and parallel workup leading to rapid generation of 3-arylcoumarin libraries under mild, solvent-free, and chromatography-free conditions