Regioselective Transition Metal-Free Catalytic Ring Opening of 2H-Azirines by Phenols and Naphthols; One-Pot Access to Benzo- and Naphthofurans

N-Heterocyclic Carbene/Organic Photoredox-Cocatalyzed Acyl Azolation of Alkenes with Acyl Azoles

We have developed the N-heterocyclic carbene/organic photoredox-cocatalyzed acyl azolation of styrenes using acyl azoles. The cooperative action of organic photoredox catalysis and NHC catalysis enabled C-N bond cleavage of the acyl azole and the insertion of the C-C double bond in styrene with complete regioselectivity. The radical cation species, generated by single electron oxidation of alkene, subsequently reacted with the nitrogen nucleophile and ketyl radical intermediate to accomplish insertion of alkene into the C-N bond.

A review of recent advances in anticancer activity and SAR of pyrazole derivatives

The present review serves to highlight the antitumor worth of pyrazole derivatives. Several active pyrazole-based anticancer compounds proposed by a huge number of scientists worldwide are reported. Regarding the development of novel pyrazole-based anticancer agents at a faster tone, there is a need to correlate the latest information with previously available information to understand the situation of this moiety in anticancer drug discovery studies. Herein, different anticancer pyrazoles are classified according to their mode of action at different anticancer targets. The results provided evidence that pyrazole derivatives have potential applications for the treatment of a variety of tumor types. From the study's findings, the structure-activity relationship (SAR) results demonstrated that all the compounds containing substituted pyrazole represent an important scaffold for anticancer activities. Publications in this area are increasing, and therefore, new therapeutic applications involving members of pyrazole derivatives could be discovered in the near future, as many prospects have not been sufficiently studied so far for other targets. In other words, this review provides an overview of the state of knowledge about the structural characteristics of the most recent anticancer pyrazole derivatives and their SAR with various targets. This will allow medicinal chemists to identify promising structures to guide the design and synthesis of more effective and safer anticancer candidates.

H3PO3 promoted reactions of thioamides with 2-substituted benzyl alcohols

In this study, we have investigated the reactivity of thioamides with alcohols by utilizing H3PO3 as a low-toxicity, cost-effective Brønsted acid catalyst. This report includes a methodology for the synthesis of thioesters from thioamides and 2-hydroxyaryl alcohols. Thioesters are emerging as a notable class of organic molecules due to their biological relevance, extensive use in drug discovery, and industrial applications. The diversity of the reaction protocol was further demonstrated through the S-alkylation of benzo[d]oxazole-2(3H)-thione and benzo[d]thiaazole-2(3H)-thione by the nucleophilic substitution of hydroxy-embedded arylalcohols. In absence of phenolic -OH, the reaction results were inferior. Based on control experiments, a reaction mechanism was proposed in which phenolic -OH acts as a directing group in the presence of H3PO3. Additionally, the practical utility of the reaction protocol was explored through the synthesis of structurally diverse benzothiazines from arylthioamides and 2-aminobenzyl alcohols.

Regioselective Ring Opening of Aziridines by Oximes via C-C Bond Cleavage: Access to a Library of Oxime-Ethers

A series of sulfonamido-substituted oxime-ethers have been synthesized by the reaction of donor-acceptor aziridines with aldo- and keto-oximes through C-C bond cleavage. Nucleophilic attack by an oxime hydroxyl group on the in situ-generated azomethine ylide rather than the routine cycloaddition reaction draws the novelty of the developed methodology. Selective protection of the oxime hydroxyl group is observed in the presence of phenolic -OH, which made the protocol enriched. In terms of a synthetic point of view, the uniqueness had been drawn further as it occurred at room temperature and within 30 min. Participation of a wide range of aziridines with a series of aldo- and keto-oximes made the developed methodology generalized by creating a novel library of substituted oxime-ethers.

MeOTf-catalyzed Friedel-Crafts alkylation of benzoxazolones, benzothiazolones, indolinones and benzimidazolones with activated secondary alcohols

Herein, we have revealed a methodology for the selective C-alkylation of benzoxazolones, benzothiazolones, indolinones, and benzimidazolones incorporating activated alcohols catalysed by methyltrifluoromethanesulfonate (MeOTf). This method offers a green, atom-economic alternative for the synthesis of alkylated heterocycles, producing water as the only byproduct. Alcohols, due to their abundance, ease of preparation, and environmental friendliness, have become attractive alkylating agents. The developed reaction conditions demonstrate high yields and broad applicability across various N-alkylated heterocycles, highlighting the versatility of the MeOTf catalysis. The method was also adapted for one-pot consecutive N- and C-alkylation and chemoselective C-alkylation in heterocycles containing a free -NH group. This approach provides a practical and efficient route for the functionalization of bioactive heterocyclic compounds.

Solvent- and Catalyst-Controlled Regioselective O- and N-Alkylation of 2-Pyridones by 2H-Azirines

The synthesis of O-substituted 2-hydroxypyridines and N-substituted 2-pyridones, crucial for many bioactive compounds and drugs, faces challenges due to the tautomeric nature of 2-pyridones, which complicates selective alkylation. Here we developed an efficient method for regioselective O- and N-alkylation of 2-pyridones using Bro̷nsted acid-catalyzed ring opening of 2H-azirines. The process involves triflic acid for O-alkylation and p-toluenesulfonic acid for N-alkylation, achieving high yields under optimized conditions. For O-alkylation, a variety of 2-pyridones and 2H-azirines were used, resulting in significant yields of the desired products. Similarly, for N-alkylation, the optimized conditions produced excellent yields, highlighting the method's versatility. This methodology was further demonstrated through scaled-up syntheses and subsequent transformations, showcasing its practicality for complex molecular architectures. The proposed mechanism involves the protonation of 2H-azirine, followed by a regioselective SN2-type attack and acid-catalyzed hydrolysis, leading to the desired alkylated products. This innovative approach, emphasizing Bro̷nsted acid catalysis and careful control of reaction conditions, represents a significant advancement in the selective alkylation of 2-pyridones, with broad implications for medicinal chemistry.

Bi(III)-Catalyzed Michael Addition of Tautomerizable Heterocycles with α,β-Unsaturated Carbonyl Compounds: Regioselective Construction of C-N Bonds

A Bi(III)-catalyzed synthetic strategy for regioselective construction of C-N bonds via a simple Michael addition reaction is reported. A wide range of tautomerizable heterocycles such as benzoxazolones, benzothiazolones, benzimidazolinones, indolinones, and 2-pyridones along with α,β-unsaturated carbonyls (ketones and esters) are employed to create a library of corresponding N-alkylated derivatives exclusively. High regioselectivity, high atom economy, and the participation of a range of tautomerizable heterocycles highlight the uniqueness and generality of the developed methodology.

Regioselective Brønsted acid catalyzed ring opening of aziridines by phenols and thiophenols; a gateway to access functionalized indolines, indoles, benzothiazines, dihydrobenzo-thiazines, benzo-oxazines and benzochromenes

Brønsted acid catalyzed regioselective ring opening of aziridines by phenols and thiophenols have been reported. Involvement of a series of aziridines with a range of phenols and thiophenols offer the generality of the reported protocol. Completion of the reaction at room temperature within very short time brings the uniqueness of the developed technique. To emphasis on the application of the developed methodology, the products have been used for the further synthesis of a range of useful and novel heterocyclic molecules such as indolines, indoles, benzothiazines, dihydrobenzothiazines, benzo-oxazines and benzochromenes.

Brønsted acid-catalyzed regioselective ring opening of 2H-azirines by 2-mercaptopyridines and related heterocycles; one pot access to imidazo[1,2-a]pyridines and imidazo[2,1-b]thiazoles

A catalytic and versatile synthetic method for the synthesis of imidazo[1,2-a]pyridines has been developed. Brønsted acid-catalysis plays a major role in the regioselective ring opening of 2H-azirines. Nucleophilic attack via the N-centre of mercaptopyridines and their analogues, followed by cyclisation by cleaving the C-S bond, allowed a library of imidazo[1,2-a]pyridines and related heterocycles to be built. The reaction protocol has been applied to various 2H-azirines, 2-mercaptopyridines, and thiazole-2-thiols, illustrating the generality of reaction conditions. The practical applications include the synthesis of pharmaceuticals, such as anti-tumor agents. This study introduces a novel approach to the synthesis of functional molecules with extensive potential.

DMF as an amine source: iron-catalyzed cyclization of 2H-azirines to imidazoles

A novel method has been developed for the synthesis of 1-methyl-4,5-diaryl-1H-imidazoles through Fe(II)-catalyzed cyclization of 2H-azirines and N,N-dimethylformamide (DMF) as an amine source. This transformation involves the cleavage of C-N and CN double bonds and the construction of new C-N and CN double bonds. The reaction has readily available starting materials, a wide range of substrates and mild reaction conditions. In addition, the reaction also facilitated the convenient synthesis of 1-methyl-2,4,5-triaryl-1H-imidazoles.