Perfluoroalkyl Aziridines with Ruthenium Porphyrin Carbene Intermediates

Trifluoromethylnitrone: a versatile building block for synthesizing trifluoromethyl-containing heterocyclic compounds

This review explores the significance of trifluoromethylnitrones in synthesizing fluorine-containing compounds, with a particular focus on trifluoromethylated heterocycles. It explores the versatility of trifluoromethylnitrones, especially in [3 + 2] cycloaddition reactions, highlighting their unique reactivity with various dienophile substrates. Trifluoromethylnitrones are valuable precursors for the rapid synthesis of medicinally important trifluoromethylated heterocycles, including isoxazolidines, dihydroisoxazoles, oxathiazolidines, β-lactams, and aziridines. These heterocycles, in turn, serve as synthons for synthesizing trifluoromethylated lactams and aminoalcohols. Additionally, nitrone chemistry extends to synthesizing trifluoromethylated nucleosides and trifluorinated organoborane heterocycles, demonstrating their versatility. While sharing similarities with trifluorodiazoethane reactivity, trifluoromethylnitrones offer distinct advantages by enabling the synthesis of heterocycles typically inaccessible with trifluorodiazoethane.

Three-Component Synthesis of Di-Keto Aziridines and Highly Functionalized Alkenes from Sulfoxonium Ylides, Nitrosoarenes, and Alkynes

A catalyst-free one-pot three-component method of sulfoxonium ylides, nitrosoarenes, and alkynes for the synthesis of highly functionalized di-keto aziridines and alkenes is described. This strategy features the catalyst-free and additive-free approach, the employment of safe, more stable, and readily accessible sulfoxonium ylides, which bear a much wider substrate scope as starting materials. In terms of terminal alkynes, a cascade reaction of nitrone formation/1,3-diploar cycloaddition/Baldwin rearrangement is involved to afford a wide variety of di-keto aziridines. However, highly functionalized alkenes could be obtained instead of di-keto aziridines through the same nitrone formation/1,3-diploar cycloaddition and another different rearrangement reaction when internal alkynes are employed as starting materials.

A Convergent, Modular Approach to Trifluoromethyl-Bearing 5-Membered Rings via Catalytic C(sp3 )-H Activation

Trifluoromethyl-bearing 5-membered rings are prevalent in bioactive molecules, but modular approaches to these compounds by functionalization of robust C(sp³ )-H bonds in a direct and selective manner are extremely challenging. Herein we report the rhodium-catalyzed α-CF₃ -α-alkyl carbene insertion into C(sp³ )-H bonds of a broad range of substrates to access 7 types of CF₃ -bearing saturated 5-membered carbo- and heterocycles. The reaction is particularly effective for benzylic C-H insertion exerting good site-, diastereo- and enantiocontrol, and applicable to the synthesis of chiral CF₃ analogues of bioactive molecules. Ruthenium α-CF₃ -α-alkyl carbene complexes underwent stoichiometric reactions to give C-H insertion products, lending evidence for the involvement of metal α-CF₃ -α-alkyl carbene species in the catalytic cycle. DFT calculations revealed that the π⋅⋅⋅π attraction and intra-carbene C-H⋅⋅⋅F hydrogen bond elucidate the origin of selectivity of the benzylic C-H insertion reactions.

Aziridination Reactivity of a Manganese(II) Complex with a Bulky Chelating Bis(Alkoxide) Ligand

Treatment of Mn(N(SiMe₃)₂)₂(THF)₂ with bulky chelating bis(alkoxide) ligand [1,1′:4′,1′′-terphenyl]-2,2′′-diylbis(diphenylmethanol) (H₂[O-terphenyl-O]^Ph) formed a seesaw manganese(II) complex Mn[O-terphenyl-O]^Ph(THF)₂, characterized by structural, spectroscopic, magnetic, and analytical methods. The reactivity of Mn[O-terphenyl-O]^Ph(THF)₂ with various nitrene precursors was investigated. No reaction was observed between Mn[O-terphenyl-O]^Ph(THF)₂ and aryl azides. In contrast, the treatment of Mn[O-terphenyl-O]^Ph(THF)₂ with iminoiodinane PhINTs (Ts = p-toluenesulfonyl) was consistent with the formation of a metal-nitrene complex. In the presence of styrene, the reaction led to the formation of aziridine. Combining varying ratios of styrene and PhINTs in different solvents with 10 mol% of Mn[O-terphenyl-O]^Ph(THF)₂ at room temperature produced 2-phenylaziridine in up to a 79% yield. Exploration of the reactivity of Mn[O-terphenyl-O]^Ph(THF)₂ with various olefins revealed (1) moderate aziridination yields for p-substituted styrenes, irrespective of the electronic nature of the substituent; (2) moderate yield for 1,1′-disubstituted α-methylstyrene; (3) no aziridination for aliphatic α-olefins; (4) complex product mixtures for the β-substituted styrenes. DFT calculations suggest that iminoiodinane is oxidatively added upon binding to Mn, and the resulting formal imido intermediate has a high-spin Mn(III) center antiferromagnetically coupled to an imidyl radical. This imidyl radical reacts with styrene to form a sextet intermediate that readily reductively eliminates the formation of a sextet Mn(II) aziridine complex.

Cascade synthetic strategies opening access to medicinal-relevant aliphatic 3- and 4-membered N-heterocyclic scaffolds

Cascade reactions are often 'employed' by nature to construct structurally diverse nitrogen-containing heterocycles in a highly stereoselective fashion, i.e., secondary metabolites important for pharmacy. Nitrogen-containing heterocycles of three- and four-membered rings, as standalone and bicyclic compounds, inhibit different enzymes and are pharmacophores of approved drugs or drug candidates considered in many therapies, e.g. anticancer, antibacterial or antiviral. Domino transformations are in most cases in line with modern green chemistry concepts due to atom economy, one-pot procedures often without use the protective groups, time-saving and at markedly lower costs than multistep transformations. The tandem approaches can help to obtain novel N-heterocyclic scaffolds, functionalized according to structural requirements of the target in cells, taking into account the nature of functional group and stereochemistry. On the other hand cascade strategies allow to modify small N-heterocyclic rings in a systematic way, which is beneficial for structure-activity relationship (SAR) analyses. This review is focused on the biological relevance of the N-heterocyclic scaffolds with smaller 3- and 4-membered rings among approved drugs and leading structures of drug candidates. The cascade synthetic strategies offering N-heterocyclic scaffolds, at relatively good yields and high stereoselectivity, are discussed here. The review covers mainly years from 2015 to 2021.

Iron porphyrin-catalyzed N-trifluoroethylation of anilines with 2,2,2-trifluoroethylamine hydrochloride in aqueous solution

An iron porphyrin-catalyzed N-trifluoroethylation of anilines has been developed with 2,2,2-trifluoroethylamine hydrochloride as the fluorine source. This one-pot N–H insertion reaction is conducted via cascade diazotization/N-trifluoroethylation reactions. The developed transformation can afford a wide range of N-trifluoroethylated anilines in good yields using readily available primary amines and secondary anilines as starting materials.

An iron porphyrin-catalyzed N-trifluoroethylation of anilines has been developed with 2,2,2-trifluoroethylamine hydrochloride as the fluorine source.

Synthesis of Fluoro-, Monofluoromethyl-, Difluoromethyl-, and Trifluoromethyl-Substituted Three-Membered Rings

This Minireview describes recent advances toward the synthesis of fluoro-, monofluoromethyl-, difluoromethyl-, and trifluoromethyl-substituted three-membered rings such as cyclopropanes, aziridines, epoxides, episulfides, cyclopropenes, and 2 H-azirines. The main synthetic methodologies since 2016 for cyclopropanes and since 2010 for the other three-membered rings are reported.

Synthesis of spirocyclic Δ4-isoxazolines via [3 + 2] cycloaddition of indanone-derived ketonitrones with alkynes

A [3 + 2] cycloaddition of indanone-derived nitrones and alkynes under mild conditions is developed, allowing facile synthesis of spirocyclicindenyl isoxazolines with structural diversity. The sequential protocol of generated in situ ketonitrone from unsaturated ketones and N-alkylhydroxylamines is also achieved successfully, affording the desired products in considerable yield with moderate to good diastereoselectivity. Moreover, the spirocyclic product can be conveniently transformed into indenyl-based allylic alcohol and enamide.

A [3 + 2] cycloaddition of indanone-derived nitrones with alkynes under mild conditions has been developed. It is a highly efficient and straightforward method for the synthesis of diverse spirocyclicindenyl isoxazolines.

Straightforward Approach toward Multifunctionalized Aziridines via Catalyst-Free Three-Component Reactions of α-Diazoesters, Nitrosoarenes, and Alkynes

A straightforward, catalyst-free atom- and step-economical approach for the synthesis of multisubstituted 1-arylaziridine-2-carboxylates via one-pot three-component reactions of α-diazoesters, nitrosoarenes, and alkynes has been described. This method could provide facile access to a variety of multifunctionalized aziridines in up to 91% yields under mild reaction conditions and features the catalyst-free strategy and use of cheap and readily accessible starting materials.

Asymmetric synthesis of CF2-functionalized aziridines by combined strong Brønsted acid catalysis

A diastereo- and enantioselective approach to access chiral CF2-functionalized aziridines from difluorodiazoethyl phenyl sulfone (PhSO2CF2CHN2) and in situ-formed aldimines is described. This multicomponent reaction is enabled by a combined strong Brønsted acid catalytic platform consisting of a chiral disulfonimide and 2-carboxyphenylboronic acid. The optical purity of the obtained CF2-substituted aziridines could be further improved by a practical dissolution-filtration procedure.

Ru(II) porphyrins as sensitizers for DSSCs: Axial vs. peripheral carboxylate anchoring group

In this study, two porphyrin chromophores metallated with ruthenium, RuTBP and RuTBPPy, were prepared and studied as sensitizers in dye-sensitized solar cells (DSSCs). The difference between the two dyes is the position (axial vs. peripheral) of the carboxylic anchoring group. This work examines the impact of this variation towards the optical, electrochemical and photovoltaic performance of DSSCs. The thorough photophysical and photovoltaic measurements indicated that the peripherally substituted sensitizer (RuTBP) presented higher photovoltaic performance compared to RuTBPPy. More specifically, DSSCs sensitized with RuTBP and RuTBPPy displayed an overall power conversion efficiency (PCE) of 5.12% and 4.08%, respectively. The higher PCE value of the DSSC sensitized with RuTBP is mainly attributed to the enhancement of [Formula: see text] and FF values. These factors were enhanced due to the efficient dye regeneration process, the suppression of back-charge recombination reactions and the longer electron lifetimes as evidenced from the electrochemical impedance spectra.

Additive-free regio- and diastereoselective construction of fully-substituted isoxazolidines employing diazo compounds

An efficient additive-free three-component access to densely functionalized isoxazolidines using diazo compounds, nitrosoarene, and allenic esters has been uncovered.