Direct Access for the Regio- and Stereoselective Synthesis of N-Alkenylpyrazoles and Chromenopyrazoles

Kurma, Siva Hariprasad; Sridhar, Balasubramanian; Raju, B. China

doi:10.1021/acs.joc.0c02421

Cited by 19 publications

(8 citation statements)

References 58 publications

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“…Although the [NN] synthon behavior of NTHs is, indeed, a major finding reported in this current research, it is also worth mentioning that pyrazoles show a wide range of biological and pharmaceutical activities, [16] so a variety of synthetic approaches to them have been developed; [17] however, the number of methods to prepare N ‐alkenyl pyrazoles is rather limited, [10] and they are mainly based in the direct addition of N ‐unsubstituted pyrazoles to alkynes [18] . Therefore, the development of new protocols to access N ‐alkenyl pyrazoles involving the de novo construction of the pyrazole ring is highly valued.…”

Section: Introductionmentioning

confidence: 92%

“…[7] In addition, the only example to date of a reaction involving both tosylhydrazones and Fischer carbene complexes, reported by J. Wang, describes the coupling between aromatic aldehyde derived tosylhydrazones and methoxy aryl chromium carbene complexes for the synthesis of 1,2-diarylethanones (Scheme 1b). [8] NTHs have shown indeed a chameleonic behavior in their reactions with alkynes, operating either as synthons of three atom units ([CNN] synthons, which is the most usual manner) to form pyrazoles in [3 + 2] cycloaddition reactions [9,10] or as synthons of a carbon atom ([C] synthons) in cyclopropenation reactions, [11] depending mainly on the nature of the tosylhydrazone (Scheme 1c). They also can act as [C] synthons with alkenes [12] and fullerenes [13] to form cyclopropanes.…”

Section: Introductionmentioning

confidence: 99%

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N‐Tosylhydrazones as [N,N] Synthons in Heterocyclic Chemistry: Synthesis of 3,5‐Disubstituted N‐Alkenyl‐1H‐pyrazoles

Velázquez‐Stavínov,

Piedra,

Gutiérrez‐Collar

et al. 2024

Adv Synth Catal

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A new mode of reactivity of N‐sulfonylhydrazones towards alkynes is described: ketone‐derived N‐tosylhydrazones (NTHs) bearing α‐H atoms behave as [NN] synthons in their reactions with alkoxy alkynyl Fischer carbene complexes (FCCs) and only the two N atoms are incorporated into the newly formed pyrazole ring. The scope of the reaction, leading to 5‐methoxy‐N‐alkenyl pyrazoles, proved to be wide regarding both partners; thus, a variety of aryl and primary, secondary, and tertiary alkyl substituents are tolerated within the FCC, while aryl alkyl NTHs, symmetric and asymmetric dialkyl NTHs and NTHs derived of cyclic ketones can be also employed. In addition, the reaction can be performed at large scale and applied for late‐stage diversification of natural products. A reasonable reaction mechanism is also proposed, which is supported by deuteration experiments and DFT calculations.

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

N‐Tosylhydrazones as [N,N] Synthons in Heterocyclic Chemistry: Synthesis of 3,5‐Disubstituted N‐Alkenyl‐1H‐pyrazoles

Velázquez‐Stavínov,

Piedra,

Gutiérrez‐Collar

et al. 2024

Adv Synth Catal

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“…Bhimapaka and co-workers 40 reported an exceptionally regioselective and stereoselective strategy for the preparation of N -alkenylpyrazoles 5 (Scheme 1 ) and chromenopyrazoles 7 (Scheme 2 ) by the reaction of N -tosylhydrazones 3 or salicylaldehyde N -tosylhydrazones 6 , respectively, with alkynes 4 in the presence of La(OTf) 3 . This route gave an efficient and convenient direct access to N -alkenylpyrazoles 5 and chromenopyrazoles 7 via C–O, C–C, and C–N bond formation.…”

Section: Applications Of N -Tosylhydrazonesmentioning

confidence: 99%

Recent Advances in Transition-Metal-Catalyzed Reactions of N-Tosylhydrazones

Pilania¹,

Vaishya²,

Singhal³

et al. 2022

Synthesis

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N-Tosylhydrazones are highly versatile precursors for in situ carbene formation and are frequently used in metal-catalyzed cross-coupling reactions. Due to their many applications in organic synthesis, including C–C, C–O, C–N, and C–S bond formation, N-tosylhydrazones have recently received much interest. They can be simply synthesized by reacting an aldehyde or ketone with N-tosylhydrazine to produce a solid N-tosylhydrazone, which is a ‘green’ precursor of diazo compounds. Using a suitable metal catalyst, N-tosylhydrazones show versatile substrate scope for the synthesis of substituted diaminopyrroles, chromenopyrazoles, alkenylpyrazoles, benzofuran thioethers, tetrahydropyridazines, sulfur-containing heterocycles, and benzofurans with potent biological activities and even regioselective N-functionalization reactions. Metal-catalyzed reactions of N-tosylhydrazones for the construction of bioactive heterocycles are still highly in demand. Hence, this review focuses on the recent synthetic application of N-tosylhydrazones influenced by different transition metals with notable features like simple workup procedures, gram-scale synthesis, broad substrate scope, multicomponent processes, cyclization, and carbon–heteroatom bond formation.1 Introduction2 Applications of N-Tosylhydrazones3 Conclusion

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“…[131] At almost the same time, an efficient, convenient protocol for the synthesis of N-alkenylpyrazoles and chromenopyrazoles via the reaction of N-tosylhydrazones and salicyl N-tosylhydrazones with alkynes 475 in the presence of La(OTf) 3 was achieved by the Bhimapaka group (Scheme 70). [132] This transformation involves the synthesis of five-membered heterocyclic compounds and provides a new approach to the future synthesis of heterocyclic compounds, especially in the fields of organic and medicinal chemistry. Notably, with N-tosylhydrazones and salicyl N-tosylhydrazones, the substituents can be replaced successfully.…”

Section: Acid-promoted Intermolecular Cyclizationmentioning

confidence: 99%

Update on the Synthesis of N‐Heterocycles via Cyclization of Hydrazones (2017–2021)

Meng

et al. 2021

Adv Synth Catal

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Hydrazones, as universal structural units, are useful synthons for the formation of carbonnitrogen and nitrogenÀ heteroatom bonds. Thus, they provide new methods of constructing nitrogen-containing heterocycles. In recent years, especially between 2017 and 2021, many efforts have been made to exploit hydrazone-based reactions in efforts to develop more powerful and effective pathways towards the synthesis of various multifunctional heterocyclic compounds. However, despite the tremendous amount of work that has been published over the past five years, no review has been published that summarizes the significant progress in the preparation of nitrogen heterocycles via intramolecular cyclization of hydrazones with adjacent unsaturated bonds or intermolecular cyclization of hydrazones with unsaturated systems. Therefore, this review summarizes the hydrazone-based cyclization strategies used to synthesize nitrogen-containing heterocycles over the past five years. It discusses the corresponding reaction scopes, limitations, mechanisms, and problems. Cyclization of Hydrazones with Unsaturated Systems 3.3. Cyclization of Hydrazones with Unsaturated Systems Under Metal-Free Conditions 4. Conclusion

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Direct Access for the Regio- and Stereoselective Synthesis of N-Alkenylpyrazoles and Chromenopyrazoles

Cited by 19 publications

References 58 publications

N‐Tosylhydrazones as [N,N] Synthons in Heterocyclic Chemistry: Synthesis of 3,5‐Disubstituted N‐Alkenyl‐1H‐pyrazoles

N‐Tosylhydrazones as [N,N] Synthons in Heterocyclic Chemistry: Synthesis of 3,5‐Disubstituted N‐Alkenyl‐1H‐pyrazoles

Recent Advances in Transition-Metal-Catalyzed Reactions of N-Tosylhydrazones

Update on the Synthesis of N‐Heterocycles via Cyclization of Hydrazones (2017–2021)

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