Palladium-catalyzed N-monoarylation of amidines and a one-pot synthesis of quinazoline derivatives

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.

Applications of palladium-catalyzed C-N cross-coupling reactions in pharmaceutical compounds

C-N cross-coupling bond formation reactions have become valuable approaches to synthesizing anilines and their derivatives, known as important chemical compounds. Recent developments in this field have focused on versatile catalysts, simple operation methods, and green reaction conditions. This review article presents an overview of C-N cross-coupling reactions in pharmaceutical compound synthesis reports. Selected examples of N-arylation reactions of various nitrogen-based compounds and aryl halides are defined for preparing pharmaceutical molecules.

Cu(ii)-catalyzed C-N coupling of 2-aminobenzothiazoles with boronic acids at room temperature

A Cu(ii)-catalyzed, effective C-N coupling of 2-aminobenzothiazoles with boronic acids in acetonitrile under open vessel chemistry was achieved. This protocol demonstrates the N-arylation of 2-aminobenzothiazoles with a broad range of differently substituted phenylboronic acids at room temperature and accomplishes moderate to excellent yields of the desired products. Under the optimized condition, phenylboronic acids bearing halogen at the para and meta positions were found to be more fruitful.

Construction of 1,2-dihydro-1,3,5-triazines via reactions involving amidines

1,2-Dihydro-1,3,5-triazine compounds were synthesized through three sets of reactions of amidines with, respectively, paraformaldehyde, aldehydes and N-arylnitrones under different conditions. The catalysts used in these three reactions were Cu(OAc)₂, ZnI₂ and CuCl₂·2H₂O, respectively. Most of the substrates tested for these reactions provided the target products in moderate to good yields. In the reactions involving paraformaldehyde, Cu(OAc)₂ also accelerated the release of formaldehyde from paraformaldehyde during the catalytic reaction process. In the case of the reactions involving nitrones, CuCl₂·2H₂O not only catalyzed the normal progress of the main reaction, but also promoted the reaction of nitrones to produce nitroso compounds and aldehydes.

Metal-Free Direct Access to N-Sulfonyl Amidines from Sulfonamides and Secondary Amines Involving Tandem C-N Bond Formations

We report a mild and efficient metal-free one-pot procedure for the synthesis of N-sulfonyl amidines via the direct reaction of sulfonamides with secondary amines without using any additives. A wide range of substrates with variety of functional groups is well tolerated under the reaction conditions. Preliminary mechanistic studies indicate that the secondary amine plays a dual role as a C1 source of the amidine group and an aminating agent. Synthetic utility of this method is shown in the late-stage functionalization of drug molecules on the gram scale.

Screening for amidoxime reductases in plant roots and Saccharomyces cerevisiae - Development of biocatalytic method for chemoselective amidine synthesis

The novel biocatalytic method for the synthesis of pharmaceutically relevant N-unsubstituted amidines was presented. The application of whole cells from commonly available vegetables allowed for the chemoselective reduction of the amidoxime moiety in the presence of other substituents prone to reduction or dehalogenation e.g. carbon-carbon double bond. Under optimized conditions several amidines were obtained with high yield up to 97% in aqueous medium at ambient temperature and atmospheric pressure. The practical potential of the newly developed method was shown in the preparative synthesis of anti-parasitic drug, phenamidine. Moreover, for the first time the enantioselective bioreduction of chiral racemic amidoximes to the corresponding amidines has been shown. The developed sustainable biocatalytic protocol fulfils the green chemistry rules and no application of metal catalysts meets the strict requirements of the pharmaceutical industry regarding metal contamination.

Open-Air Dual-Diamination of Aromatic Aldehydes: Direct Synthesis of Azolo-Fused 1,3,5-Triazines Facilitated by Ammonium Iodide

A new and practical protocol for the synthesis of medicinally privileged azolo[1,3,5]triazines by simply heating under air has been presented. The in situ generated N-azolo amidines from commercially available aromatic aldehydes and 3-aminoazoles with ammonium iodide undergo the second diamination to accomplish the [3 + 1 + 1 + 1] heteroannulation reaction. This convenient process is appreciated by high efficiency, broad substrate scope, gram-scale synthesis, and operational simplicity under reagent-free conditions.

Direct, Late-Stage Mono-N-arylation of Pentamidine: Method Development, Mechanistic Insight, and Expedient Access to Novel Antiparastitics against Diamidine-Resistant Parasites

A selective mono‐N‐arylation strategy of amidines under Chan‐Lam conditions is described. During the reaction optimization phase, the isolation of a mononuclear Cu(II) complex provided unique mechanistic insight into the operation of Chan‐Lam mono‐N‐arylation. The scope of the process is demonstrated, and then applied to access the first mono‐N‐arylated analogues of pentamidine. Sub‐micromolar activity against kinetoplastid parasites was observed for several analogues with no cross‐resistance in pentamidine and diminazene‐resistant trypanosome strains and against Leishmania mexicana. A fluorescent mono‐N‐arylated pentamidine analogue revealed rapid cellular uptake, accumulating in parasite nuclei and the kinetoplasts. The DNA binding capability of the mono‐N‐arylated pentamidine series was confirmed by UV‐melt measurements using AT‐rich DNA. This work highlights the potential to use Chan‐Lam mono‐N‐arylation to develop therapeutic leads against diamidine‐resistant trypanosomiasis and leishmaniasis.

Catalyst-free one-pot, four-component approach for the synthesis of di- and tri-substituted N-sulfonyl formamidines

A straightforward one-pot, multicomponent approach was developed to synthesize di- and tri-substituted N-sulfonyl formamidines from sulfonyl chlorides, NaN3, ethyl propiolate, and primary/secondary amines under mild conditions without catalysts or additives. Structural analysis of the di-substituted sulfonyl formamidines indicated formation of the E-syn/anti isomeric form. Tri-substituted analogues only formed E-isomers.

Palladium(ii) N,N,O-pincer type complex-mediated dehydrogenative coupling of alcohols to quinazolines

A diverse range of quinazolines were synthesized in moderate to high yields using 0.5 mol% Pd(ii) catalyst loading under aerobic conditions.

Catalytic synthesis of functionalized amidines via cobalt-carbene radical coupling with isocyanides and amines

An atom- and step-economic multi-component cobalt-catalyzed synthesis of amidines has been reported by using amines, isocyanides, and diazo compounds as carbene sources.

Transition Metal-free Approach for the Synthesis of 2-substituted Quinazolin-4(3H)-one via Anhydrous Magnesium Perchlorate

Background:

A convenient and efficient methodology for the synthesis of quinazolin- 4(3H)-ones from simple and readily available 2-amino benzamides and aromatic aldehydes in ethanol using Magnesium perchlorate are being reported in the present study. Good to excellent isolated yields (68-95%) of the corresponding 2-substituted quinazolinones were obtained under mild reaction conditions with excellent functional group tolerance. The affordability of the catalyst, the wide availability of the starting materials, transition metal free synthesis and the simplicity of the procedure renders the present methodology useful in organic synthesis.

Objective:

A maneuver methodology developed for the synthesis of quinazolin-4(3H)-ones via using Magnesium perchlorate from 2-amino benzamides and aromatic aldehydes in ethanol.

Methods:

10% mol anhydrous Magnesium perchlorate in presence of ethanol give to simply rapid formation of Quinazolin-4(3H)-ones from 1 mole of 2-amino benzamides and 1 mole of aromatic aldehydes.

Results:

Screening results of Anti-leishmanial showed that out of the synthesized series of 12 compounds, compounds 3c, 3d, 3g, 3h and 3i showed significant antileishmanial activities (L. donavani) with IC50 values 8.39, 9.37, 9.43, 7.1 and 8.7 μM.

Conclusion:

In summary, we have developed convenient synthesis of quinazolin-4(3H)-one, from simple and easily available precursor employing anhydrous Mg(ClO4)2 under green conditions.

Base-promoted Lewis acid catalyzed synthesis of quinazoline derivatives

A one-pot protocol has been developed for the synthesis of quinazolinones from amide-oxazolines with TsCl via a cyclic 1,3-azaoxonium intermediate and 6π electron cyclization in the presence of a Lewis acid and base. The process is operationally simple and has a broad substrate scope. This method provides a unique strategy for the construction of quinazolinones.

Copper-Catalyzed Coupling of Sulfonamides with Alkylamines: Synthesis of (E)-N-Sulfonylformamidines

Herein, we describe an efficient copper-catalyzed coupling of sulfonamides with alkylamines to synthesize (E)-N-sulfonylformamidines. The reaction is accomplished under mild conditions without the use of a corrosive acid or base as an additive. It tolerates a broad scope of substrates and generates the products with exclusive (E)-stereoselectivity.

Efficient Copper-Catalyzed Multicomponent Synthesis of N-Acyl Amidines via Acyl Nitrenes

Direct synthetic routes to amidines are desired, as they are widely present in many biologically active compounds and organometallic complexes. N-Acyl amidines in particular can be used as a starting material for the synthesis of heterocycles and have several other applications. Here, we describe a fast and practical copper-catalyzed three-component reaction of aryl acetylenes, amines, and easily accessible 1,4,2-dioxazol-5-ones to N-acyl amidines, generating CO₂ as the only byproduct. Transformation of the dioxazolones on the Cu catalyst generates acyl nitrenes that rapidly insert into the copper acetylide Cu–C bond rather than undergoing an undesired Curtius rearrangement. For nonaromatic dioxazolones, [Cu(OAc)(Xantphos)] is a superior catalyst for this transformation, leading to full substrate conversion within 10 min. For the direct synthesis of N-benzoyl amidine derivatives from aromatic dioxazolones, [Cu(OAc)(Xantphos)] proved to be inactive, but moderate to good yields were obtained when using simple copper(I) iodide (CuI) as the catalyst. Mechanistic studies revealed the aerobic instability of one of the intermediates at low catalyst loadings, but the reaction could still be performed in air for most substrates when using catalyst loadings of 5 mol %. The herein reported procedure not only provides a new, practical, and direct route to N-acyl amidines but also represents a new type of C–N bond formation.

Direct synthesis of 2-oxo-acetamidines from methyl ketones, aromatic amines and DMF via copper-catalyzed C(sp3)-H amidination

A convenient method for the synthesis of 2-oxo-acetamidines from methyl ketones using aromatic amines and DMF as nitrogen sources is reported via copper-catalyzed C(sp3)-H amidination. Various methyl ketones react readily with aromatic amines and DMF, producing 2-oxo-acetamidines in yields of 47 to 92%. This protocol features the simultaneous formation of C-N and C[double bond, length as m-dash]N bonds using DMF and aromatic amines as two different nitrogen sources. It thus provides an efficient approach to construct acyclic amidines via three C(sp3)-H bond amidination. Based on the preliminary experiments, a plausible mechanism of this transformation is disclosed.

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.

Heterogeneous oxidative synthesis of quinazolines over OMS-2 under ligand-free conditions

OMS-2 is employed to synthesize heterocycles through selective oxidation without the help of ligands.

Pd-Catalyzed tandem reaction of N-(2-cyanoaryl)benzamides with arylboronic acids: synthesis of quinazolines

A Pd-catalyzed tandem reaction of N-(2-cyanoaryl)benzamides with arylboronic acids for the synthesis of quinazolines has been reported.

Cp*Rh(iii)-catalyzed annulation of N-methoxybenzamide with 1,4,2-bisoxazol-5-one toward 2-aryl quinazolin-4(3H)-one derivatives

A [Cp*Rh^III]-catalyzed annulation of N-methoxybenzamide with 1,4,2-bisoxazol-5-one was developed, affording a series of 2-aryl quinazolin-4(3H)-one derivatives.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions

Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Copper(i) chloride promoted Csp2–N cross-coupling of 1,2-di(pyrimidin-2-yl) disulfides with amines: an efficient approach to obtain C2-amino functionalized pyrimidines

The copper(i)-promoted cross-coupling of 1,2-di(pyrimidin-2-yl) disulfides with aromatic amines and aliphatic amines to deliver C–N coupling products in moderate to good yields is reported in this paper.

Synthesis of quinazolines and quinazolinones via palladium-mediated approach

Quinazoline derivatives have drawn attention in the field of heterocyclic chemistry because of their unique skeleton and interesting biological applications. This review summarizes the recent palladium-catalyzed reactions used to construct quinazoline and its related 4(3H)-quinazolinone analogues. The mechanisms of some Pd-catalyzed reactions are also discussed.