Rh(III)- and Zn(II)-Catalyzed Synthesis of Quinazoline N-Oxides via C–H Amidation–Cyclization of Oximes

Recent Advances in Metal-Catalyzed Approaches for the Synthesis of Quinazoline Derivatives

Quinazolines are an important class of heterocyclic compounds that have proven their significance, especially in the field of organic synthesis and medicinal chemistry because of their wide range of biological and pharmacological properties. Thus, numerous synthetic methods have been developed for the synthesis of quinazolines and their derivatives. This review article briefly outlines the new synthetic methods for compounds containing the quinazoline scaffold employing transition metal-catalyzed reactions.

A Review on the Synthesis and Chemical Transformation of Quinazoline 3-Oxides

The synthesis of quinazoline 3-oxides and their derivatives has attracted considerable attention due to their reactivity as intermediates in the synthesis of quinazoline analogues and their ring-expanded derivatives. Despite this, there is no comprehensive review dedicated to the synthesis and chemical transformation of these biologically relevant azaaromatic oxides. This review aims to provide an up-to-date record of the synthesis of quinazoline 3-oxides and their chemical transformation. It is hoped that this information will help medicinal chemistry researchers to design and synthesize new derivatives or analogues to treat various diseases.

Construction of N-Acyliminophosphoranes via Iron(II)-Catalyzed Imidization of Phosphines with N-Acyloxyamides

Employing FeCl₂ as a cheap and readily available catalyst, a facile imidization of phosphines with N-acyloxyamides is described, affording synthetically useful N-acyliminophosphoranes with high functional group tolerance. The transformation is easily performed under an air atmosphere at room temperature and could be scaled up to gram scale with a catalyst loading of 1 mol %. The iminophosphoranyl moiety in the product was further utilized as an effective directing group for controllable ortho C(sp²)-H bond amidations under Rh(III) catalysis.

Rhodium-Catalyzed C-H Activation-Based Construction of Axially and Centrally Chiral Indenes through Two Discrete Insertions

Reported herein is asymmetric [3+2] annulation of arylnitrones with different classes of alkynes catalyzed by chiral rhodium(III) complexes, with the nitrone acting as an electrophilic directing group. Three classes of chiral indenes/indenones have been effectively constructed, depending on the nature of the substrates. The coupling system features mild reaction conditions, excellent enantioselectivity, and high atom-economy. In particular, the coupling of N-benzylnitrones and different classes of sterically hindered alkynes afforded C-C or C-N atropochiral pentatomic biaryls with a C-centered point-chirality in excellent enantio- and diastereoselectivity (45 examples, average 95.6 % ee). These chiral center and axis are disposed in a distal fashion and they are constructed via two distinct migratory insertions that are stereo-determining and are under catalyst control.

Chemical Insights Into the Synthetic Chemistry of Quinazolines: Recent Advances

In medicinal chemistry, one of the most significant heterocyclic compounds are quinazolines, possessing broad range of biological properties such as anti-bacterial, anti-fungal, anti-HIV, anti-cancer, anti-inflammatory, and analgesic potencies. Owing to its numerous potential applications, in the past two decades, there is an increase in the importance of designing novel quinazolines, exploring promising routes to synthesize quinazolines, investigating different properties of quinazolines, and seeking for potential applications of quinazolines. The present review article describes synthesis of quinazolines via eco-friendly, mild, atom-efficient, multi-component synthetic strategies reported in the literature. The discussion is divided into different parts as per the key methods involved in the formation of quinazoline skeletons, aiming to provide readers an effective methodology to a better understanding. Consideration has been taken to cover the most recent references. Expectedly, the review will be advantageous in future research for synthesizing quinazolines and developing more promising synthetic approaches.

Synthesis of Sulfimides and N-Allyl-N-(thio)amides by Ru(II)-Catalyzed Nitrene Transfer Reactions of N-Acyloxyamides

The N-acyloxyamides were employed as effective N-acyl nitrene precursors in reactions with thioethers under the catalysis of a commercially available Ru(II) complex, from which a variety of sulfimides were synthesized efficiently and mildly. If an allyl group is contained in the thioether precursor, the [2,3]-sigmatropic rearrangement of the sulfimide occurs simultaneously and the N-allyl-N-(thio)amides were obtained as the final products. Preliminary mechanistic studies indicated that the Ru-nitrenoid species should be a key intermediate in the transformation.

Vinylene carbonate: beyond the ethyne surrogate in rhodium-catalyzed annulation with amidines toward 4-methylquinazolines

Vinylene carbonate: acetylation reagent rather than ethyne surrogate in rhodium-catalyzed annulation with amidines toward 4-methylquinazolines.

Synthesis of Benzothiadiazine-1-oxides by Rhodium-Catalyzed C-H Amidation/Cyclization

A rhodium-catalyzed C-H amidation/cyclization sequence provides benzothiadiazine-1-oxides from sulfoximines and 1,4,2-dioxazol-5-ones in good yields. The reaction is characterized by a high functional group tolerance and, in contrast to most previous transformations of this type, is well-suited for S-alkyl-S-aryl-substituted sulfoximines.

Rhodium(III)-catalyzed C4-amidation of indole-oximes with dioxazolones via C-H activation

A novel method for the Rh(iii)-catalyzed oxime-directed C-H amidation of indoles with dioxazolones has been developed. This strategy provides an exclusive site selectivity and the directing group can be easily removed. This transformation features a wide substrate scope, good functional group tolerance and excellent yields, and may serve as a significant tool to construct structurally diverse indole derivatives for the screening of potential pharmaceuticals in the future.

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.

Rhodium(iii)-catalyzed ortho-C-H amidation of 2-arylindazoles with a dioxazolone as an amidating reagent

A simple and efficient method for the directed amidation of a wide range of 2-arylindazoles has been established for the first time through a rhodium-catalyzed C-H activation reaction with alkyl, aryl and heteroaryl dioxazolones. A series of N-(2-(2H-indazol-2-yl)phenyl)acetamide derivatives were synthesized in excellent yields. A mechanistic study was conducted to describe C-H bond cleavage which is likely to be involved in the rate determining step.

Rhodium(iii)-catalyzed synthesis of spirocyclic isoindole N-oxides and isobenzofuranones via C–H activation and spiroannulation

Rhodium(iii)-catalyzed C–H activation of oximes and benzoic acids has been realized in oxidative annulation with quinone diazides for synthesis of spirocycles.

Rhodium(III)-Catalyzed Regioselective C(sp2)-H Functionalization of 7-Arylpyrazolo[1,5-a]pyrimidines with Dioxazolones as Amidating Agents

Rh(III)-catalyzed C-H functionalization of 7-arylpyrazolo[1,5-a]pyrimidines was developed wherein the pyrazolo[1,5-a]pyrimidine moiety is reported for the first time to direct the C-H bond activation. Various 7-arylpyrazolo[1,5-a]pyrimidines underwent smooth C-H amidation with alkyl-, aryl-, and heteroaryl-substituted dioxazolones to afford the products in moderate to good yields. Mechanistic studies suggest that a six-membered rhodacycle intermediate involving N1 might play a key role in the regioselective catalytic cycle.

Rhodium(iii)-catalyzed diverse [4 + 1] annulation of arenes with 1,3-enynes via sp3/sp2 C-H activation and 1,4-rhodium migration

Nitrogen-rich heterocyclic compounds have a profound impact on human health. Despite the numerous synthetic methods, diversified, step-economic, and general synthesis of heterocycles remains limited. C-H bond functionalization catalyzed by rhodium(iii) cyclopentadienyls has proven to be a powerful strategy in the synthesis of diversified heterocycles. Herein we describe rhodium(iii)-catalyzed sp2 and sp3 C-H activation-oxidative annulations between aromatic substrates and 1,3-enynes, where alkenyl-to-allyl 1,4-rhodium(iii) migration enabled the generation of electrophilic rhodium(iii) π-allyls via remote C-H functionalization. Subsequent nucleophilic trapping of these species by various sp2-hybridized N-nucleophiles delivered three classes (external salts, inner salts, and neutral azacycles) of five-membered azacycles bearing a tetrasubstituted saturated carbon center, as a result of [4 + 1] annulation with the alkyne being a one-carbon synthon. All the reactions proceeded under relatively mild conditions with broad substrate scope, high efficiency, and excellent regioselectivity. The synthetic applications of this protocol have also been demonstrated, and experimental studies have been performed to support the proposed mechanism.

Rhodium-Catalyzed C(sp2 )- or C(sp3 )-H Bond Functionalization Assisted by Removable Directing Groups

In recent years, transition-metal-catalyzed C-H activation has become a key strategy in the field of organic synthesis. Rhodium complexes are widely used as catalysts in a variety of C-H functionalization reactions because of their high reactivity and selectivity. The availability of a number of rhodium complexes in various oxidation states enables diverse reaction patterns to be obtained. Regioselectivity, an important issue in C-H activation chemistry, can be accomplished by using a directing group to assist the reaction. However, to obtain the target functionalized compounds, it is also necessary to use a directing group that can be easily removed. A wide range of directed C-H functionalization reactions catalyzed by rhodium complexes have been reported to date. In this Review, we discuss Rh-catalyzed C-H functionalization reactions that are aided by the use of a removable directing group such as phenol, amine, aldehyde, ketones, ester, acid, sulfonic acid, and N-heteroaromatic derivatives.

Synthesis of quinazoline-3-oxides via a Pd(ii) catalyzed azide-isocyanide coupling/cyclocondensation reaction

A novel and efficient protocol concerning palladium catalyzing the three-component reaction of 2-azidobenzaldehyde, isocyanide, and hydroxylamine hydrochloride is developed. This method allows the rapid elaboration of quinazoline 3-oxides in a one-pot fashion. The 3-CR mainly involves concatenation of azide-isocyanide denitrogenative coupling, condensation with hydroxylamine and 6-exo-dig cyclization. The salient features of the methodology are operational simplicity, use of milder reaction conditions, being devoid of any additives such as oxidants (redox neutral) or base, and releasing N2 and H2O as the byproducts.

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Cp*CoIII-catalyzed formal [4+2] cycloaddition of benzamides to afford quinazolinone derivatives

A Cp*Co^III-catalyzed arene C–H bond amidation/annulation of benzamides was developed to afford quinazolinone derivatives in one-pot with high yields and broad substrate scope.

Rhodium(iii)-catalyzed cascade reactions of benzoic acids with dioxazolones: discovery of 2,5-substituted benzoxazinones as AIE molecules

Rhodium-catalyzed cascade reactions of benzoic acids with 1,4,2-dioxazol-5-ones afford 2,5-substituted benzoxazinones, which exhibited AIE properties with an ESIPT phenomenon.

Recent Progress on Cyclic Nitrenoid Precursors in Transition-Metal-Catalyzed Nitrene-Transfer Reactions

Nitrene-transfer reactions are powerful synthetic tools for the direct incorporation of nitrogen atoms into organic molecules. The discovery of novel nitrene-transfer reactions has been dominantly supported not only by improvements in transition-metal catalysts but also by the employment of novel precursors of nitrenoids. Since pioneering work involving the use of organic azides and iminoiodinanes as practical synthetic tools for nitrogen-containing compounds was reported, a new approach using various N-heterocycles containing strain energy or a weak bond has emerged. In this review, we briefly summarize the history of nitrene-transfer chemistry from the viewpoint of its precursors. In particular, the use of N-heterocycles such as 2H-azirines, 1,4,2-dioxazol-5-ones, 1,2,4-oxadiazol-5-ones, isoxazol-5(4H)-ones, and isoxazoles is comprehensively described, showing the recent remarkable progress in this chemistry.

Rh(III)-Catalyzed One-Pot Synthesis of Benzimidazoquinazolines via C-H Amidation-Cyclization of N-LG-2-phenylbenzoimidazoles

An efficient protocol to synthesize substituted benzo[4,5]imidazo[1,2- c]quinazolines starting from N-LG-2-phenylbenzoimidazole and dioxazolones catalyzed by Rh(III) or Ir(III) has been developed. Various substituted benzo[4,5]imidazo[1,2- c]quinazolines could be easily provided in up to 99% yield. A large range of substrates and functional groups are compatible for this transformation. This method features low catalyst loading, acid-free conditions, and low solvent consumption.

Rh(III)-Catalyzed C-C Coupling of Diverse Arenes and 4-Acyl-1-sulfonyltriazoles via C-H Activation

4-Acyl-1-sulfonyltriazoles act as versatile carbene reagents in Cp*Rh(III)-catalyzed ortho-selective coupling with arenes via C-H activation. The coupling led to olefination with possible cyclization, depending on the nature of the arene.