Current Organic Synthesis - Volume 13, Issue 6, 2016

Benzofuran derivatives are the scaffold of many natural products, many of which are biologically active and/or found to have high potential as pharmacological agents. Therefore, benzofuran derivatives are expected to be invaluable moieties as far as biology and pharmacology are concerned. In this review, we try to highlight the recent advances in the synthetic approaches to a wide variety of its derivatives in particular those showing biological activity.

Propylene carbonate (PC) is a polar aprotic substance with very similar physicochemical characteristics to the organic solvents traditionally used for organic synthesis, such as acetonitrile and acetone. Therefore, PC is beginning to be used as a “green” sustainable alternative solvent for chemical transformations. PC is a low toxicity, non-corrosive colourless liquid with a high boiling point and low vapour pressure. It is biodegradable and economical, allowing its large-scale use. PC can be prepared by a reaction between propylene epoxide and carbon dioxide with 100% atomic economy. The easy preparation of propylene epoxide and the use of an available, abundant, economical, and renewable source of carbon, such as CO2, make this process one of the best routes for the synthesis of PC. Therefore, we present in this review numerous catalytic systems that have been studied to improve the efficiency of this reaction. Certain interesting examples of reactions using PC are found in the literature, of which we discuss asymmetric hydrogenation, hydrosilylation, asymmetric aldol reactions, the asymmetric synthesis of cyanohydrins, the synthesis of heterocyclic compounds, such as bisindole and tetrahydroquinoline, the hydroacylation of alkynes, α-hydrazination reactions, oxidations, the Sonogashira reaction, allylic alkylation and asymmetric amination, the Heck reaction, enzymatic kinetic resolution, and isomerisation-hydroformylation reactions.

The Diels-Alder (DA) reaction has been applied to the total synthesis of natural products. It can get good yields because of high stereoselectivity and regioselectivity. Herein, the DA reaction catalyzed by Lewis acids was introduced, and some total syntheses of natural products from 2013 to 2015 using DA reaction were also illustrated and analyzed.

Organic semiconductors are significant as highly prospective materials of reasonable costs for use in a broad range of organic electronics, i.e., light-emitting instruments, FETs, as well as solar cells. Semiconductors built with organic materials maintain their processing ability as related to polymeric units while also retaining their optical characteristics, i.e., elevated absorption coefficients and field-effect mobility close to the value of formless silicon. The explanation of valid arrangement-feature connections becomes crucial in the engineering of useful and efficient semiconducting organic materials. This article summarizes the most recent discoveries in the grafting of semiconducting polymeric structures onto different solids for electronic tools, and also presents the effects of adaptable tails in semiconducting organics. This includes information on how size is impacted, odd-even results, substitution and localization, end groups, branching, and also discusses the connections stemming from the halogenation of organic semiconductors.

The new ruthenium vinylidene catalysts with general formula [RuCl2(=C=CHR)(PCy3)2] (R= -p- C6H4CF3 (I), -p-C6H4F (II) and -C6H9 (III)) were used in the cross-metathesis degradation of natural rubber (NR) using essential oils, β-pinene and d-limonene as chain transfer agents (CTAs). The isolated isoprene oligomer products with molecular weight around Mn x 104 g/mol were obtained when the reactions were carried out at 50 °C. An enhancement of the catalytic activity was achieved at 80 °C showing a decrease in the molecular weights of products with around Mn x 103 g/mol. Experiments also demonstrated that the poly(styrene-co-butadiene) (SB) depolymerized in the presence of essential oils and d-limonene as CTAs by vinylidene catalysts to give the butadiene oligomers with molecular weight values around Mn = 295-698 g/mol. According to GS/MS (EI) analysis, the main products of the degradation of SB with d-limonene were limonene-terminated butadiene oligomers with m = 1-3.

Novel palladium-catalyzed cascade reaction of 2-methylindoles with 2- iodobenzyl bromide in the system Pd(OAc)2 / Xantphos / t-BuOK / toluene leading to indole- fused tricyclo[7,3,1,02,7] trideca-2(7),3,5-triene ring system was presented. Palladium catalyzed reaction of 2-methylindoles with 6-bromo-5-bromomethylbenzo[1,3] dioxole leads to 3,3-bis(6-bromobenzo[1,3]dioxol-5-ylmethyl)-2-methyl-3H-indoles.

This contribution discloses a simple and efficient procedure using environmentally benign supported cobalt nanocatalyst for the synthesis of bis(indolyl)methanes under solventfree conditions. The supported cobalt nanocatalyst exhibited excellent activity and stability and it could be reused for at least ten times without any loss of activity, providing an efficient and stable catalytic system for the synthesis of a number of important bis(indolyl)methanes.

An efficient, green and facile protocol for the synthesis of pyranopyrazole derivatives through the reaction of aromatic aldehydes, malononitrile, hydrazine hydrate and ethyl acetoacetate was developed using Ru loaded hydroxyapatite (Ru-CaHAp) as catalyst. The eco-friendly one-pot reactions in an ethanol-water mixture are fast (≈15 min) and occur at room temperature. The catalyst was fully characterized by various techniques. The chemical structures of the synthesized compounds were identified and confirmed by 1H, 15N and 13C NMR, FT-IR and HR-MS spectral data. The noteworthy advantages offered by this method are an environmentally-friendly simple procedure, mild conditions, short reaction times, recycling of catalyst and good to excellent (89 to 98%) yield of products.

A series of epoxyesters were lactonized by HClO4 to give corresponding -hydroxy-γ-lactones as a mixture of diastereoisomers: trans and cis. The mixtures of products were separated via column chromatography. The lactones synthesized were screened for anticancer activity against D17 and U2-OS cell lines. Only the trans isomer with naphthyl ring was found to exhibit significant activity against both cell lines.

New series of thiazoles and thiadiazines incorporated with pyrazole ring were synthesized via the reaction of 2-(1-(4-cyano-1,5-diphenyl-1H-pyrazol-3-yl)ethylidene) hydrazine-carbothioamide or 4-imino-7-methyl- 2,3-diphenyl-2H-pyrazolo[3,4-d]pyridazine-5(4H)-carbothiohydrazide with different reagents. The structures of all tautomeric forms of the newly synthesized compounds were confirmed on the basis of spectral data aided with DFT and semi-empirical calculations.