Pummerer rearrangement using bis(p-nitrophenyl) phosphorazidate as an azidation reagent: A novel synthesis of azidomethyl sulfides

A novel method for the synthesis of azidomethyl sulfides by Pummerer rearrangement using bis(p-nitrophenyl) phosphorazidate (p-NO₂DPPA) as an azidation reagent was developed. Various methyl sulfoxides were converted into the corresponding azidomethyl sulfides. Importantly, this reaction enables the preparation of azidomethyl sulfides without the use of toxic or explosive azide sources.     

Regioselective synthesis of 4- and 5-oxazole-phosphine oxides and -phosphonates from 2H-azirines and acyl chlorides

A simple and efficient regioselective synthesis of 4-oxazole-phosphine oxides 11 and -phosphonates 12 from 2H-azirine-phosphine oxides 1 and -phosphonates 6 is described. The key step for the synthesis of oxazoles 11 is a base-mediated ring closure of vinylogous α-aminophosphorus compounds derived from phosphine oxides 4 and from phosphonates 8. These derivatives 4 and 8 are obtained by reaction of functionalized azirines 1 and 6 with acyl chlorides 2 and subsequent acid-catalyzed ring opening of N-acylaziridine-phosphine oxides 3 and -phosphonates 7. Regioselective thermal ring cleavage of N-acylaziridine-phosphine oxides 3 leads α-chloro-β-(N-acylamido)-phosphine oxides 13 and their treatment with bases gives 5-oxazole-phosphine oxides 16.     

Fe(III)-catalyzed oxidative coupling of alkylnitriles with aromatic carboxylic acids: Facile access to cyanomethyl esters

The first oxidative coupling of alkylnitriles with aromatic carboxylic acids using di-tert-butyl peroxide (DTBP) as oxidant was achieved under the catalysis of ionic Fe(III) complexes bearing an imidazolinium cation. This protocol features nontoxic iron catalysis, direct α-C(sp³)–H bond oxidative esterification of alkylnitriles, non-prefunctionalized starting materials, and a broad substrate scope with outstanding steric hindrance tolerance, providing a novel, straightforward, and green approach toward cyanomethyl ester synthesis.     

Facile and scalable synthesis of nanostructured Fe2O3 using ionic liquid-assisted ball milling for high-performance pseudocapacitors

In this study, we report that ionic liquid (IL)-assisted ball milling of iron precursors in the absence of any reagent resulted in the scalable production of IL/Fe₂O₃ hybrids with a favourable morphology (high surface area of 202 m²/g and pore size of 40nm) for supercapacitor applications. During ball milling process, ILs are played role as structure guiding templates for construction of rod-like pore containing Fe₂O₃ and surface functionalities for IL/Fe₂O₃ hybrids, resulting in good wettability and enhanced ion transfer. These attractive features of IL/Fe₂O₃ hybrids make them excellent candidate pseudocapacitive electrode materials that exhibit a high specific capacitance of 230 F/g at a current density of 1 A/g, fast and reversible charge/discharge rates (∼71% retention at 15 A/g), and excellent long-term cycle stability (∼100% retention over 10000 cycles).     

An efficient synthesis of N-protected threo (2R,3S)-3-amino-1,2-epoxy phenylbutane

A precise and versatile method was developed for the synthesis of threo amino epoxide derivatives, which are useful intermediates for protease inhibitors. It involves the diastereoselective reduction of the carbonyl group of γ-N,N-dibenzyl amino α-hydroxy β-keto sulfide prepared from an amino acid, and its subsequent stereospecific conversion to an amino epoxide via acetoxy halogenation in high yield.     

Comparisons of O-acylation and Friedel-Crafts acylation of phenols and acyl chlorides and Fries rearrangement of phenyl esters in trifluoromethanesulfonic acid: effective synthesis of optically active homotyrosines

Reactions involving phenol derivatives and acyl chlorides have to be controlled for competitive O-acylations and C-acylations (Friedel-Crafts acylations and Fries rearrangements) in acidic condition. The extent for these reactions in trifluoromethanesulfonic acid (TfOH), which is used as catalyst and solvent, is examined. Although diluted TfOH was needed for effective O-acylation, concentrated TfOH was required for effective C-acylations in mild condition. These results have been applied to the novel synthesis of homotyrosine derivatives. Both Fries rearrangement of N-TFA-Asp(OBn)-OMe and Friedel-Crafts acylation of phenol with N-TFA-Asp(Cl)-OMe in TfOH afforded the homotyrosine skeleton, followed by reduction and deprotection afforded homotyrosines maintaining stereochemistry of Asp as an optically pure form.     

碳膜包覆的氧化铁纳米颗粒:一种高效的芳硝基化合物加氢催化剂

铁是地球上最丰富的元素之一,它在生命反应中起到至关重要的作用.目前,铁基催化剂广泛应用于合成氨、费托合成、NOx的选择性催化还原等.最近,铁因其含量丰富、价格低廉、无毒等优势而在多相催化方面引起了重点关注.最新研究发现,铁基催化剂在甲烷直接偶联制乙烯、氧还原以及芳硝基化合物的选择性加氢等领域具有突出表现,其中芳硝基化合物选择性加氢是一类具有重要应用前景的反应,这是因为苯胺(AN)是一种重要的精细化学品和有机中间体,广泛用于医药、染料、农药等行业,苯胺的年产量超过了400万吨,目前使用的催化剂主要有Raney Ni、负载镍、Ru/SnO2及少量铂碳、钯碳催化剂.但是,在Ni基催化剂上,硝基苯加氢主要经过间接缩合途径,同时会伴有氧化偶氮苯(AOB)、偶氮苯(AB)和氢化偶氮苯(HAB)等副产物生成,这些高沸点的副产物会带来一系列问题,如产物分离困难、产品纯度较低以及催化剂失活等.在这种情况下,为了加速苯胺生成,工业上一般采用过量的Raney Ni催化剂.贵金属(如Pt,Pd和Ru等)对催化芳硝基化合物加氢具有极高的活性,且苯胺的生成主要经过直接加氢途径.然而,由于成本过高,贵金属催化剂的大规模应用还存在一定的困难.本文采用简易的方法制备了一种铁基催化剂,在这个催化剂中氧化铁纳米颗粒被碳膜包覆并嵌入至平板碳中(Fe2O3@G-C).该催化剂由活性炭、苯胺及醋酸亚铁热解所得.通过扫描电镜(SEM)、拉曼光谱(Raman)及X射线衍射(XRD)分析,我们证实在原始碳颗粒上形成了新的碳膜.同时高倍透射电镜图也清楚地揭示了氧化铁纳米颗粒被碳膜包覆的结构.实验发现,Fe2O3@G-C-900催化剂(900oC热解所得)在芳硝基化合物选择性加氢反应中具有很高的活性.在2 MPa H2,70oC条件下反应2 h,硝基苯(NB)转化率达到95.4%,苯胺选择性达到99.1%,远远高于其他载体(活性炭、SiO2、Al2O3和MgO)负载的铁基催化剂.表征结果发现,Fe2O3@G-C-900催化剂的高活性可能与其具有较大的比表面积(573.7 m2/g)、孔体积(0.22 cm3/g,孔径小于2 nm)、高度分散的氧化铁纳米颗粒以及氧化铁纳米颗粒和其表面碳膜的协同作用密切相关.此外,催化剂中引入的氮原子不仅可以在包覆的碳膜上形成缺陷,也能进一步增强包覆在氧化铁纳米颗粒表面的碳膜的催化活性.通过对Fe2O3@G-C-900催化剂在硝基苯加氢反应中的循环使用活性的考察,发现该催化剂在循环使用5次后,仍具有良好的活性.更重要的是,在Fe2O3@G-C-900催化剂上硝基苯的加氢主要是直接途径,反应中没有高沸点AOB,AB和HAB等副产物生成.鉴于Fe2O3@G-C-900催化剂对NB加氢具有优异的活性,我们还进行了一系列含有不同取代基团的芳硝基化合物的加氢实验,发现对位取代的底物相对于间位及邻位的底物更容易发生加氢还原反应,这应归因于该催化剂的孔径较小(0.52 nm).这些研究方法可以扩展至其他金属催化剂的制备,以促进高效益和可持续的工业生产的发展.     

A general and efficient reduction of acyl chlorides to aldehydes by Sm(0)/Bu3P

A facile and efficient reduction of aromatic and aliphatic acyl chlorides to their corresponding aldehydes in the presence of Sm(0)/Bu₃P has been developed with broad scope. This method prevents over reduction of products, that is, the over-reduction of aldehydes to alcohols.     

Visible-light-mediated cascade difunctionalization/cyclization of alkynoates with acyl chlorides for synthesis of 3-acylcoumarins

A new visible-light-mediated radical cyclization of alkynoates with acyl chlorides is described for the one-pot construction of diverse 3-acylcoumarins with high efficiency and selectivity. This method is successful by sequential difunctionalization of an alkynes CC triple bond with the CCl bonds of acyl chloride and aromatic C(sp²)H bonds. The cyclization is proposed to simultaneously form two new carbon–carbon bonds, and involves radical acylation, 5-exo-trig cyclization, and ester migration.     

One-carbon ring-expansion of 2-substituted cyclohexanones via lithium- and magnesium β-oxido carbenoid rearrangement: a new synthesis of 2,7-disubstituted and 2,2,7-trisubstituted cycloheptanones

Lithium α-sulfinyl carbanion of 1-chloroethyl p-tolyl sulfoxide was reacted with 2-substituted cyclohexanones to afford adducts in good yields. The adducts were treated with LDA or t-BuMgCl to give lithium or magnesium alkoxides, which were treated with t-BuLi or i-PrMgCl to afford one-carbon ring-expanded 2,7-disubstituted cycloheptanones through β-oxido carbenoids. Interestingly, 2,3-disubstituted cycloheptanones were obtained in a trace amount or were not obtained at all. The enolate intermediates of this reaction were found to be able to get trapped with electrophiles to give 2,2,7-trisubstituted cycloheptanones in moderate to good yields. This method is very useful for the synthesis of 2,7-disubstituted cycloheptanones and 2,2,7-trisubstituted cycloheptanones from 2-substituted cyclohexanones in only two steps.     

A convenient method for the preparation of aromatic ketones from acyl chlorides and arylzinc bromides using a cobalt catalysis

Aromatic ketones are synthesized efficiently via cobalt catalyzed cross-coupling reaction between arylzinc bromides and acid chlorides. Arylzinc bromides prepared chemically via a cobalt catalysis undergo coupling without additional catalyst unlike their electrochemical analogs.     

Highly-efficient and recyclable nanosized MCM-41 anchored palladium bipyridyl complex-catalyzed coupling of acyl chlorides and terminal alkynes for the formation of ynones

A highly-efficient and practical method for the formation of ynones from a variety of acyl chlorides and terminal alkynes catalyzed by a nanosized MCM-41 anchored palladium bipyridyl complex is described herein. Aroyl, heteroaroyl, and alkyl acyl chlorides were easily coupled with terminal alkynes, giving good to high isolated yields in the presence of a very low catalyst loading (0.002-0.1 mol % Pd) in Et₃N or diisopropylethylamine at 50 °C. Furthermore, the reaction scale was up to 150 mmol for a single batch reaction, providing the potential for practically synthetic application. After centrifugation, the supported catalyst was able to be recycled and reused several times with only a slight decrease in activity.     

Fe3O4 as a magnetically reusable Fenton nanocatalyst for the oxidation of thiols to sulfonic acid and sulfides to sulfoxides and sulfones

In this study, the oxidation of thiols to sulfonic acids and sulfides to sulfoxides and sulfones was carried out in the presence of Fe₃O₄/H₂O₂ as an efficient heterogeneous Fenton system. The products were obtained in good to excellent yields and short reaction times. Further results showed that the heterogeneous catalyst could be recovered easily using an external magnetic field and reused several times without any loss of its catalytic activity.     

Facile preparation of Fe2O3 nanoparticles mediated by Centaurea alba extract and assessment of the anti-atherosclerotic properties

This research work attempts to synthesize iron nanoparticles with Centaurea alba extract. The reported synthesis method serves to be more effective over conventional physical and chemical methods, which is found to be cost effective, recyclable, biocompatible and prevents oxidation of iron oxide nanoparticle as well.As the extract of Centaurea alba possess high content of flavonoids, tannins and phenolic acids, it thereby prevents the oxidation and accumulation iron oxide NPs. The morphological features of the obtained nanoparticle were determined by TEM and SEM imaging techniques. Furthermore, various spectroscopic techniques including UV-Vis, FT-IR has been evaluated.As a part of cellular and molecular studies, the prepared FeNPs was subjected to MTT assay for 48h on normal (HUVEC) cells to evaluate its cytotoxicity. The IC50 of FeNPs and BHT against DPPH free radicals were 287 and 191 µg/mL respectively. Male Wistar rats were selected as the model organism for the in vivo studies and has been categorized into 6 groups, where normal diet was provided to the control group, cholesterol diet was provided to sham group (HCD: 1.50% cholesterol and 24.00% fat) and HCD was provided to other groups. FeNPs were infused at low (100µg Kg^-1), moderate (200 µg/Kg) and maximum (400 µg/Kg) doses via gavages. Additionally, atorvastatin (10 mg Kg^-1) was provided to the last group through gavages with HCD. Six months has been fixed as a study period for all the groups. Various parameters including total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) was assessed in the blood samples of the test organism at the end of the period. Furthermore, sections of coronary artery and aortic arteries were subjected to histopathological examinations, which showed increase in vessel wall thickness in HCD group, however FeNPstreated groups showed no significant pathological changes. Decrease in TG, TC and LDL-C was observed upon treatment of HCD animals with FeNPs.     

Reaction of 2-alkyl pyridine N-oxide derivatives with Mosher’s acyl chloride: first example of stereoselective Boekelheide rearrangement

Treatment of 2-alkyl pyridine N-oxides with acylating reagents represents an established procedure for the introduction of oxygen functionality into alkyl group at the ortho position of N heteroaromatic rings. We have reported the first example of asymmetric Boekelheide rearrangement applied to a set of 2-alkyl-pyridine N-oxide derivatives using (R) Mosher’s acyl chloride as activator of the rearrangement to give, after hydrolysis, enantiomerically enriched 1-(2-pyridinyl)alkyl alcohol. Diastereoselectivity of the process was studied at low temperatures in different solvents, and was supported by a preliminary in silico modeling.     

A short microwave-assisted synthesis of tetrahydroisoquinolin-pyrrolopyridinones by a triple process: Ugi-3CR-aza Diels-Alder/S-oxidation/Pummerer

A series of tetrahydroisoquinolin-pyrrolopyridinones were prepared from an easily accessible aldehyde, a commercially available amine, a readily isolable isonitrile, and maleic anhydride via a triple process: Ugi-3CR-aza Diels-Alder/S-oxidation/Pummerer. The combination of a multicomponent Ugi-type reaction with other post-functionalization processes provides a powerful tool for the preparation of fused polyheterocyclic compounds.     

Studies on the aza-Claisen rearrangement of 4,5-dihydroxylated allylic trichloroacetimidates: the stereoselective synthesis of (2R,3S)- and (2S,3S)-2-amino-3,4-dihydroxybutyric acids

Two new synthetic approaches, involving substrate directed aza-Claisen rearrangements and aza-Claisen rearrangements mediated by chiral Pd(II) catalysts, have been developed for the stereoselective synthesis of (2R,3S)-2-amino-3,4-dihydroxybutyric acid, a dihydroxylated α-amino acid from the edible mushroom, Lyophyllum ulmarium and its (2S,3S)-unnatural diastereomer.