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.

Regioselective Synthesis of N-Vinyl Pyrazoles from Vinyl Sulfonium Salts with Diazo Compounds

Herein, we develop a base-promoted regioselective synthesis of N-vinyl pyrazoles from vinyl sulfonium salts with diazo compounds. This metal-free synthetic protocol provides an efficient and practical approach to diverse N-vinyl pyrazoles in good to excellent yields under mild conditions. The reaction appears to experience a [3 + 2] annulation of vinyl sulfonium salts and diazo anions rather than diazo compounds, followed by N-vinylation.

Revisiting the Chemistry of Vinylpyrazoles: Properties, Synthesis, and Reactivity

Vinylpyrazoles, also known as pyrazolyl olefins, are interesting motifs in organic chemistry but have been overlooked. This review describes the properties and synthetic routes of vinylpyrazoles and highlights their versatility as building blocks for the construction of more complex organic molecules. Concerning the reactivity of vinylpyrazoles, the topics surveyed herein include their use in cycloaddition reactions, free-radical polymerizations, halogenation and hydrohalogenation reactions, and more recently in transition-metal-catalyzed reactions, among other transformations. The current state of the art about vinylpyrazoles is presented with an eye to future developments regarding the chemistry of these interesting compounds. Styrylpyrazoles were not considered in this review, as they were the subject of a previous review article published in 2020.

Cyclization of arylhydrazones of cross-conjugated enynones: synthesis of luminescent styryl-1H-pyrazoles and propenyl-1H-pyrazoles

On the basis of available ethynyl vinyl ketones and arylhydrazines, the authors have developed the two-stage synthesis method for styrylpyrazoles possessing fluorescent abilities, as well as the gram-scale synthesis method for fluorescent probes.

Recent advances in pyrazole synthesis employing diazo compounds and synthetic analogues

This review summarizes the recent developments in the construction of pyrazoles using diazo compounds, nitrile imines and their synthetic equivalents.

Stereoselective Synthesis of Tri- and Tetrasubstituted Olefins via 1,6-Additions of Diazo Compounds and Their Precursors to p-Quinone Methides

Reactions of para-quinone methides (p-QMs) with α-diazo-β-ketosulfones and their corresponding esters as well as simple β-dicarbonyl compounds and β-ketosulfones have been carried out under basic conditions. While the reaction of diazosulfone with p-QMs afforded trisubstituted olefins via deacylative 1,6-addition and elimination, α-diazo-β-ketoesters and various active methylene compounds such as 1,3-dicarbonyls and β-ketosulfones afforded tetrasubstituted olefins via 1,6-addition and aerial oxidation. These simple, environmentally benign, and mechanistically diverse protocols provided the products in moderate to excellent yields and selectivities.

Regioselective [3 + 2] Cycloaddition Reaction of 3-Alkynoates with Seyferth-Gilbert Reagent

A Et₃N-triggered regioselective [3 + 2] cycloaddition reaction of 3-alkynoates with Seyferth-Gilbert reagent has been developed to furnish a series of trisubstituted pyrazole-3-phosphonates. A one-pot cycloaddition/alkylation sequence further offered access to the corresponding fully substituted pyrazoles.

Styrylpyrazoles: Properties, Synthesis and Transformations

The pyrazole nucleus and its reduced forms, pyrazolines and pyrazolidine, are privileged scaffolds in medicinal chemistry due to their remarkable biological activities. A huge number of pyrazole derivatives have been studied and reported over time. This review article gives an overview of pyrazole derivatives that contain a styryl (2-arylvinyl) group linked in different positions of the pyrazole backbone. Although there are studies on the synthesis of styrylpyrazoles dating back to the 1970s and even earlier, this type of compound has rarely been studied. This timely review intends to summarize the properties, biological activity, methods of synthesis and transformation of styrylpyrazoles; thus, highlighting the interest and huge potential for application of this kind of compound.

The Bestmann-Ohira Reagent and Related Diazo Compounds for the Synthesis of Azaheterocycles

Azaheterocycles are one of the most prevalent classes of compounds present in numerous bioactive compounds, natural products, and agrochemicals, and undoubtedly, new methods to access them are always in high demand. Among the methods available, the 1,3-dipolar cycloaddition reactions involving diazo compounds are particularly attractive because of their ability to rapidly construct densely functionalized azaheterocycles in a regioselective manner. In this context, the Bestmann-Ohira reagent has become a well-known reagent for the 1,3-dipolar cycloaddition reactions to produce phosphonylated heterocycles, besides its widespread use as a homologating agent for the conversion of aldehydes to alkynes. This account details our efforts toward broadening the synthetic utility of the Bestmann-Ohira reagent and related compounds for the preparation of azaheterocycles such as pyrazoles, spirooxindoles, triazoles, triazolines, and spiropyrazolines, emphasizing on domino multicomponent reactions employing readily available feedstock reagents.

Catalytic Direct Regioselective Synthesis of Phosphonylated Tetrazoles from Aryl Diazonium Salts and Seyferth-Gilbert Reagent

Here we report a Ag-catalyzed [3 + 2] cycloaddition reaction between aryl diazonium salts and Seyferth-Gilbert reagent in a regioselective manner. This operationally simple transformation proceeds in an atom-economical way under mild reaction conditions, providing facile access to a broad set of phosphonylated tetrazoles. The synthetic utility of this method is further showcased by a straightforward procedure from upstream aromatic amines, denitrogenation transformations, and preparation of a phosphonylated drug scaffold.

Synthesis of Functionalized Pyrazoles via 1,3-Dipolar Cycloaddition of α-Diazo-β-ketophosphonates, Sufones and Esters with Electron-Deficient Alkenes

1,3-Dipolar cycloaddition of diazo compounds with olefinic substrates is a promising atom-economic strategy for the construction of functionalized pyrazoles. Over the last few years, our group has been engaged in the synthesis of phosphonyl/sulfonylpyrazoles and pyrazole esters by employing Bestmann-Ohira Reagent (BOR) and its sulfur and ester analogs as 1,3-dipole precursors with various dipolarophiles. This account describes the novel synthetic methods developed in our laboratory, in the perspective of closely related work by others, for the synthesis of phosphonyl/sulfonylpyrazoles, pyrazole esters and the total synthesis of Withasomnine, a natural product, by using 1,3-dipolar cycloaddition as the key step.

Fluoride-Mediated Dephosphonylation of α-Diazo-β-carbonyl Phosphonates

The possibility of fluoride-mediated selective dephosphonylation of α-diazo-β-carbonyl phosphonates such as the Ohira-Bestmann reagent has been proposed and executed. The resulting α-diazocarbonyl intermediates undergo a (3 + 2)-cycloaddition at room temperature with conjugated olefins and benzynes. Interestingly, under the current conditions, the resulting cycloaddition products underwent either N-acylation (with excess α-diazo-β-carbonyl phosphonates) or Michael addition (with conjugated olefins).

Partially Saturated Bicyclic Heteroaromatics as an sp(3) -Enriched Fragment Collection

Fragment‐based lead generation has proven to be an effective means of identifying high‐quality lead compounds for drug discovery programs. However, the fragment screening sets often used are principally comprised of sp²‐rich aromatic compounds, which limits the structural (and hence biological) diversity of the library. Herein, we describe strategies for the synthesis of a series of partially saturated bicyclic heteroaromatic scaffolds with enhanced sp³ character. Subsequent derivatization led to a fragment collection featuring regio‐ and stereo‐controlled introduction of substituents on the saturated ring system, often with formation of new stereocenters.

Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates

Multicomponent reactions (MCRs) are one of the most important processes for the preparation of highly functionalized organic compounds in modern synthetic chemistry. As shown in this review, they play an important role in organophosphorus chemistry where phosphorus reagents are used as substrates for the synthesis of a wide range of phosphorylated heterocycles. In this article, an overview about multicomponent reactions used for the synthesis of heterocyclic compounds bearing a phosphonate group on the ring is given.

Metal-Free Three-Component Domino Approach to Phosphonylated Triazolines and Triazoles

An efficient, three-component domino reaction between aldehydes, amines, and the Bestmann-Ohira reagent is reported that enables a general, mild, and straightforward access to 1,4,5-trisubstituted 1,2,3-triazolines and triazoles. The reaction proceeds through a domino-condensation/1,3-dipolar cycloaddition sequence to afford the triazoline derivatives with excellent diastereoselectivity. Moreover, when both amine and aldehyde employed for this reaction are aromatic, a spontaneous oxidation afforded 1,4,5-trisubstituted triazoles in moderate yields.

An efficient one pot regioselective synthesis of a 3,3'-spiro-phosphonylpyrazole-oxindole framework via base mediated [1,3]-dipolar cycloaddition reaction of the Bestmann-Ohira reagent with methyleneindolinones

A one pot, highly regioselective synthesis of racemic 3,3'-spiro-phosphonylpyrazole-oxindole by 1,3-dipolar cycloaddition of an in situ generated anion of dialkyl 1-diazomethylphosphonate from the Bestmann-Ohira reagent (BOR) & methyleneindolinones has been developed. The synthesis affords the highly functionalized pyrazole scaffolds in good yields with excellent regioselectivity under mild reaction conditions within a short reaction time.

Stereoselective construction of functionalized tetracyclic and pentacyclic coumarinopyranpyrazole/pyrimidinedione/coumarin scaffolds using a solid-state melt reaction

An assembly of tetra / pentacyclic hybrid scaffolds have been synthesized for the first time using a solid-state melt reaction in a stereoselective fashion with excellent yields.

Substrate-controlled product-selectivity in the reaction of the Bestmann–Ohira reagent with N-unprotected isatin-derived olefins

A mild and efficient reaction of the Bestmann–Ohira reagent withN-unprotected isatin-derived olefins has been developed for the selective synthesis of spiro-phosphonylpyrazoline-oxindoles and phosphonylpyrazoloquinazolinones.