Microwave-promoted syntheses of quinazolines and dihydroquinazolines from 2-aminoarylalkanone O-phenyl oximes

Cooperation between the Cu+ and Cu2+ species in CuCoAl layered double hydroxide and the substrate promoting effect afford a really simple protocol for the efficient synthesis of quinazolines

In this study, a really simple and efficient catalytic protocol for the construction of quinazolines from alcohol and diamine has been developed based on CuCoAl layered double hydroxide (CuCoAl-LDH). The developed CuCoAl-LDH catalyst could accelerate the cascade reactions without any additives and tolerate various alcohols with satisfactory yields. Cooperation between the Cu+ and Cu2+ species in CuCoAl-LDH was observed in the cascade reaction, and they are believed to be responsible for the oxidation of alcohol and dehydrogenation of the intermediate, respectively. The promoting effect of the substrate diamine was observed in the oxidation of alcohol, which simplifies the reaction system by eliminating the requirement for a base additive. The catalytic system exhibited highly practical potential for the synthesis of quinazolines, as demonstrated through recyclability investigations and scale-up experiments. A possible catalytic mechanism has been proposed based on a series of control experiments and EPR analysis.

Visible-light photocatalyzed C-N bond activation of tertiary amines: a three-component approach to synthesize quinazolines

A metal-free three-component approach has been developed to prepare 2,4-disubstituted quinazolines from o-acylanilines, trialkylamines and ammonium chloride under visible-light using eosin Y as the photocatalyst. The notable features of this work include (i) the use of tertiary amines as an alkyl synthon and triethanolamine as a C2-OH synthon; (ii) good functional group tolerance with 52%-98% yields; (iii) proof of concept with o-amino benzaldehyde as a substrate to deliver 2-methyl quinazoline 3pa; and (iv) gram-scale synthesis of compounds 3ga, 3ja and 3ma. A reductive quenching mechanism was proposed based on the control studies and redox potential values.

Arene Ruthenium(II)-Catalyzed Sustainable Synthesis of 2,4-Disubstituted Quinazolines via Acceptorless Dual Dehydrogenative Coupling of Alcohols

We demonstrate an efficient and sustainable strategy for the direct synthesis of 2,4-disubstituted quinazolines by arene Ru(II)benzhydrazone complex via the eco-friendly sequential acceptorless dehydrogenative coupling of 2-aminobenzhydrol derivatives and benzyl alcohols for the first time. The new ruthenium(II) complex of the general formula [(η6-p-cymene)Ru(L1)Cl] (L1-acenaphthenequinone hydrazone) has been synthesized and characterized by analytical, spectroscopic, and single-crystal X-ray diffraction techniques. A broad spectrum of 2,4-disubstituted quinazolines have been successfully derived (25 examples) from 2-aminobenzhydrol derivatives with various benzyl alcohols using 1 mol % of catalyst loading in the presence of NH4OAc. The present protocol is highly selective and produces a maximum yield of 95% under mild reaction conditions. The different reaction intermediates detected through control experiments such as aldehyde, 2-aminobenzophenone, benzylidene(amino)phenylmethanone, and 1,2-dihydroquinazoline are isolated and authenticated by the NMR study. Gratifyingly, the coupling reaction is a simple and atom economic with the release of water and hydrogen gas as the only byproducts. A gram-scale synthesis of 2-(4-methoxyphenyl)-4-phenylquinazoline illustrates the synthetic utility of the present protocol.

Room temperature ligand-free Cu2O-H2O2 catalyzed tandem oxidative synthesis of quinazoline-4(3H)-one and quinazoline derivatives

An efficient and simple copper catalytic system has been developed for the synthesis of medicinally important 2-substituted quinazoline-4(3H)-ones from 2-aminobenzonitrile and benzyl alcohol derivatives and additionally 2-substituted quinazolines from 2-aminobenzylamine and benzaldehyde derivatives. Mild oxidant H₂O₂ was utilized, providing excellent product yields. The molecular structure of one of the compounds was substantiated through SC-XRD. The versatility of the protocol was demonstrated through gram-scale syntheses.

Transformation of Waste Toner Powder into Valuable Fe2O3 Nanoparticles for the Preparation of Recyclable Co(II)-NH2-SiO2@Fe2O3 and Its Applications in the Synthesis of Polyhydroquinoline and Quinazoline Derivatives

Ecological recycling of waste materials by converting them into valuable nanomaterials can be considered a great opportunity for management and fortification of the environment. This article deals with the environment-friendly synthesis of Fe₂O₃ nanoparticles (composed of α-Fe₂O₃ and γ-Fe₂O₃) using waste toner powder (WTP) via calcination. Fe₂O₃ nanoparticles were then coated with silica using TEOS, functionalized with silane (APTMS), and immobilized with Co(II) to get the desired biocompatible and cost-effective catalyst, i.e., Co(II)-NH₂-SiO₂@Fe₂O₃. The structural features in terms of evaluation of morphology, particle size, presence of functional groups, polycrystallinity, and metal content over the surface were determined by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (P-XRD), field emission gun-scanning electron microscopy (FEG-SEM), energy-dispersive X-ray analysis (EDX), high resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), Brunauer-Emmett-Teller (BET) analysis, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) studies. XPS confirmed the (II) oxidation state of Co, and ICP-AES and EDX supported the loading of Co(II) over the surface of the support. P-XRD proved the polycrystalline nature of the Fe₂O₃ core and even after functionalization. In comparison to previously reported methods, Co(II)-NH₂-SiO₂@Fe₂O₃ provides an eco-friendly procedure for the synthesis of polyhydroquinoline and quinazoline derivatives with several advantages such as a short reaction time and high yield. Polyhydroquinoline and quinazoline derivatives are important scaffolds in pharmacologically active compounds. Moreover, the developed nanocatalyst was recyclable, and HR-TEM and P-XRD confirmed the agglomeration in the recycled catalyst resulted in a decrease in yield after the fifth run. The present protocol provides a new strategy of recycling e-waste into a heterogeneous nanocatalyst for the synthesis of heterocycles via multicomponent reactions. This made the synthesized catalyst convincingly more superior to other previously reported catalysts for organic transformations.

Preparation of 4-arylquinazolines with o-(N-alkyl,N-p-tosyl)aminobenzonitriles, aryllithiums, and NIS

The treatment of o-(N-alkyl,N-p-tosyl)aminobenzonitriles with aryllithiums, followed by the reaction with water, NIS under irradiation with a fluorescent lamp, and then ^tBuOK gave 2-alkyl-4-arylquinazolines or 4-arylquinazolines in good to moderate yields. The present reaction proceeds through the formation of N-iodoimines from imines with NIS, the generation of iminyl radicals, the 1,6-H shift by iminyl radicals, the cyclization via 6-exo-tet mode, and finally the elimination of p-toluenesulfinate to generate 2-alkyl-4-arylquinazolines or 4-arylquinazolines.

Efficient solvent- and temperature-tuned access to aldoxime ethers and phenolic functions by Pd-catalyzed C–O cross-coupling of aldoximes with aryl bromides and bromo-chalcones

A single method with a functionality switching option, to access oxime ethers and phenols, was developed for the first time for the Pd-catalyzed C–O cross-coupling of aryl bromides and bromo-chalcones with aldoximes.

TMSOTf-catalyzed synthesis of substituted quinazolines using hexamethyldisilazane as a nitrogen source under neat and microwave irradiation conditions

An efficient synthetic route for the synthesis of substituted quinazolines under neat, metal-free and microwave irradiation conditions has been developed by using TMSOTf as an acid catalyst and HMDS as a nitrogen source.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Efficient Synthesis of Quinazolinones by Transition-Metal-Free Direct Aerobic Oxidative Cascade Annulation of Alcohols with o-Aminoarylnitriles

A mild and atom-economic method was developed for direct and efficient synthesis of quinazolinones through a transition-metal-free aerobic oxidative cascade annulation reaction of widely available o-aminoarylnitriles and alcohols. Air could be employed as an effective oxidant under mild conditions, generating water as the only byproduct. Possibly owing to the "cesium effect", the water-soluble base CsOH was found to be crucial in all key steps of the reaction mechanism. Because a wide range of substrates can be used to prepare substituted quinazolinones without contamination by transition-metal residues, this method may be of interest for application in pharmaceutical synthesis. Possible reaction paths were also proposed according to control reactions.

Iodine/potassium iodide catalyst for the synthesis of trifluoromethylated quinazolines via intramolecular cyclization of 2,2,2-trifluoro-N-benzyl-N'-arylacetimidamides

An efficient and simple protocol for the synthesis of trifluoromethylated quinazolines has been described by I₂-/KI-promoted oxidative C(sp³)-C(sp²) bond under the optimal oxidative cyclization reaction conditions. The required 2,2,2-trifluoro-N-benzyl-N'-arylacetimidamides are readily prepared from the corresponding acetimidoyl chlorides and benzylamines under a nucleophilic substitution reaction in the form of in situ. The merits of this protocol are the use of inexpensive molecular iodine, metal-free oxidative coupling and good to excellent yields.

Synthesis of 1,2-Dihydroquinazolines via Rearrangement of Indazolium Salts

A convenient synthesis of 1,2-dihydroquinazolines via rearrangement of indazolium salts was described. A mechanistic study using isotope labeling experiment revealed that the rearrangement passes through cleavage of N-N bond/ring opening after basic deprotonation of 2-benzyl in indazolium salts to yield intermediate E, which proceeds in an intramolecular N-nucleophilic addition to form the observed product. Computational analyses imply that the pathway of the rearrangement is determined by the energy barriers of the ring-closing process and the stability of the product.

Eco-friendly reactions in PEG-400: a highly efficient and green approach for stereoselective access to multisubstituted 3,4-dihydro-2(1H)-quinazolines using 2-aminobenzylamines

An efficient and stereoselective synthesis of novel 3,4-dihydro-2(1H)-quinazolines has been developed through cyclization reactions of 2-aminobenzylamines with α-oxoketene dithioacetals using PEG-400 as an inexpensive, easy to handle, non-toxic and recyclable reaction medium. The developed protocol is operationally simple and tolerates various substrates having different functionalities. This protocol features several attributes such as excellent yields, no work up, green reaction conditions, and being environmentally benign. The attractive feature of this new strategy is that all the reported final compounds have been isolated as single (E)-stereoisomeric forms, which was confirmed by 1HNMR and X-ray crystallographic studies.

Visible-light-promoted iminyl radical formation from vinyl azides: synthesis of 6-(fluoro)alkylated phenanthridines

An efficient strategy assisted by visible-light-promoted iminyl radical formation has been developed for the synthesis of 6-(fluoro)alkylated phenanthridine derivatives. In the reactions, addition of alkyl and trifluoromethyl radicals onto vinyl azides gives iminyl radicals, which then undergo intramolecular homolytic aromatic substitution leading to phenanthridines. These reactions can be carried out under mild conditions with high chemical yields and broad substrate scope.

Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals

The totality of chemical space is so immense that only a small fraction can ever be explored. Computational searching has indicated that bioactivity is associated with a comparatively small number of ring-containing structures. Pyrrole, indole, pyridine, quinoline, quinazoline and related 6-membered ring-containing aza-arenes figure prominently. This review focuses on the search for fast, efficient and environmentally friendly preparative methods for these rings with specific emphasis on iminyl radical-mediated procedures. Oxime derivatives, particularly oxime esters and oxime ethers, are attractive precursors for these radicals. Their use is described in conventional thermolytic, microwave-assisted and UV-vis based preparative procedures. Photoredox-catalyzed protocols involving designer oxime ethers are also covered. Choice can be made amongst these synthetic strategies for a wide variety of 5- and 6-membered ring heterocycles including phenanthridine and related aza-arenes. Applications to selected natural products and bioactive molecules, including trispheridine, vasconine, luotonin A and rutaecarpine, are included.

Microwave-Assisted Synthesis of Bioactive Six-Membered Heterocycles and Their Fused Analogues

This review describes the formation of six-membered heterocyclic compounds and their fused analogues under microwave activation using modern organic transformations including cyclocondensation, cycloaddition, multicomponents and other modular reactions. The review is divided according to the main heterocycle types in order of increasing complexity, starting with heterocyclic systems containing one, two and three heteroatoms and their fused analogues. Recent microwave applications are reviewed, with special focus on the chemistry of bioactive compounds. Selected examples from the 2006 to 2015 literature are discussed.

Functionalised Oximes: Emergent Precursors for Carbon-, Nitrogen- and Oxygen-Centred Radicals

Oxime derivatives are easily made, are non-hazardous and have long shelf lives. They contain weak N-O bonds that undergo homolytic scission, on appropriate thermal or photochemical stimulus, to initially release a pair of N- and O-centred radicals. This article reviews the use of these precursors for studying the structures, reactions and kinetics of the released radicals. Two classes have been exploited for radical generation; one comprises carbonyl oximes, principally oxime esters and amides, and the second comprises oxime ethers. Both classes release an iminyl radical together with an equal amount of a second oxygen-centred radical. The O-centred radicals derived from carbonyl oximes decarboxylate giving access to a variety of carbon-centred and nitrogen-centred species. Methods developed for homolytically dissociating the oxime derivatives include UV irradiation, conventional thermal and microwave heating. Photoredox catalytic methods succeed well with specially functionalised oximes and this aspect is also reviewed. Attention is also drawn to the key contributions made by EPR spectroscopy, aided by DFT computations, in elucidating the structures and dynamics of the transient intermediates.

Synthesis of quinazolines from 2-aminobenzylamines with benzylamines and N-substituted benzylamines under transition metal-free conditions

This work reports the synthesis of quinazolines from 2-aminobenzylamines with N-substituted benzylamines in the presence of molecular iodine. The developed methodology works smoothly under transition-metal free, additive free and solvent free conditions and the use of O₂ as a green oxidant makes it a greatly economical.

Magnesium iodide-catalyzed synthesis of 2-substituted quinazolines using molecular oxygen and visible light

We disclose a novel and efficient synthesis of 2-substituted quinazolines by aerobic photooxidative reaction catalyzed by magnesium iodide.

Acid catalyzed synthesis of 2-(2-aminophenyl)quinazoline-4-amine and reaction with aromatic aldehydes

The hydrochloride salt of 2-(2-aminophenyl)quinazoline-4-amine, prepared from a quinazolino[3,4-a]quinazoline, was reacted with aromatic aldehydes under conventional heating or microwave irradiation, leading to tetracyclic dihydroquinazolines.

Traceless Solid-Phase Synthesis of Trisubstituted Quinazolines

A traceless polymer-supported synthesis of 4-benzoylquinazolines was developed using the following commercially available building blocks: Fmoc-α-amino acids, 2-nitrobenzensulfonyl chlorides and α-bromoacetophenones. The acyclic intermediates underwent base-catalyzed rearrangement involving C-C and N-N bond formation followed by ring expansion and yielded resin-bound dihydroquinazoline-2-carboxylic acids. After they were released from the resin by treatment with trifluoroacetic acid, base-mediated decarboxylation produced the target quinazolines in moderate-to-high yields and purities.