Recent advances in organocatalytic atroposelective reactions

• Henrich Szabados and
• Radovan Šebesta

Beilstein J. Org. Chem. 2025, 21, 55–121, doi:10.3762/bjoc.21.6

Synthesis of extended fluorinated tripeptides based on the tetrahydropyridazine scaffold

• Thierry Milcent,
• Pascal Retailleau,
• Benoit Crousse and
• Sandrine Ongeri

Beilstein J. Org. Chem. 2024, 20, 3174–3181, doi:10.3762/bjoc.20.262

• synthesis of tripeptides incorporating new fluorinated heterocyclic hydrazino acids, based on the tetrahydropyridazine scaffold is described. Starting from simple fluorinated hydrazones, these non-proteinogenic cyclic β-amino acids were easily prepared by a zinc-catalyzed aza-Barbier reaction followed by an

• for peptide synthesis. Consequently, developing a simple and efficient methodology is still challenging. Our new strategy to synthesize these compounds is based on an aza-Barbier reaction on difluoro- or trifluoromethylated hydrazones. The thus obtained compounds will then be oxidized and cyclized in

• order to lead to the expected fluorinated tetrahydropyridazines (Figure 4). Results and Discussion First, the difluoro- and trifluoromethylated hydrazones 3a–f were synthesized by condensing the corresponding hydrazide with the fluorinated aldehyde hemiacetal 2a or 2b (Scheme 2). Benzyl and tert-butyl

C–H Trifluoromethylthiolation of aldehyde hydrazones

• Victor Levet,
• Balu Ramesh,
• Congyang Wang and
• Tatiana Besset

Beilstein J. Org. Chem. 2024, 20, 2883–2890, doi:10.3762/bjoc.20.242

• /Education Center for Excellence in Molecular Sciences Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China 10.3762/bjoc.20.242 Abstract The selective C–H trifluoromethylthiolation of aldehyde hydrazones afforded interesting fluorinated building blocks, which could be used as a

• synthetic platform. Starting from readily available (hetero)aromatic and aliphatic hydrazones, the formation of a C–SCF3 bond was achieved under oxidative and mild reaction conditions in the presence of the readily available AgSCF3 salt via a one-pot sequential process (28 examples, up to 91% yield

• ). Mechanistic investigations revealed that AgSCF3 was the active species in the transformation. Keywords: C–H bond functionalization; C–S bond formation; hydrazones; synthetic method; trifluoromethylthiolation; Introduction Fluorinated molecules are of paramount importance [1][2][3][4][5][6][7][8][9][10][11

Asymmetric organocatalytic synthesis of chiral homoallylic amines

• Nikolay S. Kondratyev and
• Andrei V. Malkov

Beilstein J. Org. Chem. 2024, 20, 2349–2377, doi:10.3762/bjoc.20.201

• separate peaks on chiral HPLC. Kinetic resolution of chiral secondary allylboronates [15][30]. (E)-Stereospecific asymmetric α-trifluoromethylallylation of cyclic imines and hydrazones [31]. Hosomi–Sakurai-type allylation of in situ-formed N-Fmoc aldimines [32]. Chiral squaramide-catalysed hydrogen bond

Multicomponent syntheses of pyrazoles via (3 + 2)-cyclocondensation and (3 + 2)-cycloaddition key steps

• Ignaz Betcke,
• Alissa C. Götzinger,
• Maryna M. Kornet and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2024, 20, 2024–2077, doi:10.3762/bjoc.20.178

• their synthesis have been extensively reviewed [93]. When hydrazones undergo cyclization with β-ketoesters or ketones, the stability of the enol form of the carbonyl compounds plays a crucial role in the reaction. Recognizing this, a series of multicomponent reactions has been developed to synthesize

• , facilitating their cyclization with intermediary formed hydrazones to yield 5-hydroxypyrazolines. After subsequent interaction with atmospheric oxygen, the product 65 is formed. This method exhibits a high degree of substituent tolerance, and aliphatic compounds generally lead to higher yields. A special

• the process for both electron-rich and electron-poor aldehydes. In addition to fully substituted pyrazoles, the method also provides access to anellated products. Lellek's team has developed an alternative method for cyclizing hydrazones. In contrast to the previously mentioned method, intermediately

Harnessing the versatility of hydrazones through electrosynthetic oxidative transformations

• Aurélie Claraz

Beilstein J. Org. Chem. 2024, 20, 1988–2004, doi:10.3762/bjoc.20.175

• Aurelie Claraz Institut de Chimie des Substances Naturelles, CNRS, Univ. Paris-Saclay, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France 10.3762/bjoc.20.175 Abstract Hydrazones are important structural motifs in organic synthesis, providing a useful molecular platform for the

• construction of valuable compounds. Electrooxidative transformations of hydrazones constitute an attractive opportunity to take advantage of the versatility of these reagents. By directly harnessing the electrical current to perform the oxidative process, a large panel of organic molecules can be accessed from

• readily available hydrazones under mild, safe and oxidant-free reaction conditions. This review presents a comprehensive overview of oxidative electrosynthetic transformations of hydrazones. It includes the construction of azacycles, the C(sp2)−H functionalization of aldehyde-derived hydrazones and the

Synthesis of 1,2,3-triazoles containing an allomaltol moiety from substituted pyrano[2,3-d]isoxazolones via base-promoted Boulton–Katritzky rearrangement

• Constantine V. Milyutin,
• Andrey N. Komogortsev and
• Boris V. Lichitsky

Beilstein J. Org. Chem. 2024, 20, 1334–1340, doi:10.3762/bjoc.20.117

• ]isoxazolone derivatives with various hydrazines was studied. It was shown that the considered process includes formation of corresponding hydrazones followed by Boulton–Katritzky rearrangement. As a result, the general method for the synthesis of substituted 1,2,3-triazoles bearing an allomaltol fragment was

• types of aforementioned structures were proved by X-ray analysis. Keywords: allomaltol; Boulton–Katritzky rearrangement; hydrazones; pyrano[2,3-d]isoxazolones; recyclization; 1,2,3-triazoles; Introduction The Boulton–Katritzky rearrangement (BKR) also known as mononuclear heterocyclic rearrangement is

• participation of hydrazones attract special attention. This reaction is a general method for the preparation of 1,2,3-triazoles bearing various substituents at position 2. Wherein, depending on the type of starting heterocycles various functional derivatives are formed. So, the well-known Boulton–Katritzky

Manganese-catalyzed C–C and C–N bond formation with alcohols via borrowing hydrogen or hydrogen auto-transfer

• Mohd Farhan Ansari,
• Atul Kumar Maurya,
• Abhishek Kumar and
• Saravanakumar Elangovan

Beilstein J. Org. Chem. 2024, 20, 1111–1166, doi:10.3762/bjoc.20.98

• hydride. In 2018, the Milstein group demonstrated a partial hydrogen-borrowing reaction with a manganese-pincer complex by coupling alcohols and hydrazine to form N-substituted hydrazones. Benzylic and aliphatic alcohols were studied with hydrazine using Mn(t-Bu-PNN)(CO)2Br (Mn5, 3 mol %) and a catalytic

• condenses with hydrazine followed by reduction and condensation with another aldehyde to afford the N-substituted hydrazones (Scheme 8). Balaraman and co-workers established a phosphine-free manganese catalyst generated in situ from a manganese precursor and a ligand for the N-alkylation of anilines with

Mild and efficient synthesis and base-promoted rearrangement of novel isoxazolo[4,5-b]pyridines

• Vladislav V. Nikol’skiy,
• Mikhail E. Minyaev,
• Maxim A. Bastrakov and
• Alexey M. Starosotnikov

Beilstein J. Org. Chem. 2024, 20, 1069–1075, doi:10.3762/bjoc.20.94

• us to try another protecting group for the formyl function, namely arylhydrazone. Thus, reactions of compounds 7a–c with a number of arylhydrazines afforded the corresponding hydrazones 11 which were not isolated and subjected to cyclization under the action of K2CO3 (Scheme 5). In most cases the

• were performed for compounds 12c and 13c,d (Figure 3; see Supporting Information File 1 for details) that allowed us to unambiguously establish the structures of both the starting hydrazones and rearrangement products. Conclusion In summary, we have developed an efficient method for the synthesis of

Synthesis of spiropyridazine-benzosultams by the [4 + 2] annulation reaction of 3-substituted benzoisothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes

• Wenqing Hao,
• Long Wang,
• Jinlei Zhang,
• Dawei Teng and
• Guorui Cao

Beilstein J. Org. Chem. 2024, 20, 280–286, doi:10.3762/bjoc.20.29

• ][20][21][22][23][24][25][26][27], which can be readily generated in situ from α-halogeno hydrazones, have been extensively applied in recent years as versatile building blocks in inverse-electron-demand Diels–Alder (IEDDA) reactions [28][29][30] to construct diverse nitrogen-containing heterocycles

• follows: 1a (1.0 mmol), 2a (1.5 mmol), Et3N (2.0 mmol), in acetonitrile at 25 °C with stirring for 2 hours (Table 1, entry 14). With the optimized reaction conditions in hand, we next investigated the scope of the current reaction (Scheme 2). As shown in Scheme 2, a series of α-halogeno hydrazones 2b–l

• was tested, resulting in the expected spiropyridazine-benzosultams 3ab–al in good to excellent yields with high diastereoselectivity. For N-benzoyl hydrazones 2b–g, the electronic effect of R3 group on the [4 + 2] annulation reaction was significant. Electron-withdrawing groups gave relatively higher

Catalytic multi-step domino and one-pot reactions

• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2024, 20, 254–256, doi:10.3762/bjoc.20.25

• of transannular cycloadditions of cycloalkenone hydrazones catalyzed by BINOL-derived phosphoric acid are reported in the Full Research Paper by Vicario, Merino, and co-workers [10]. Their methodologies can now be used to predict the reactivity of different substrates in other cycloaddition reactions

Construction of diazepine-containing spiroindolines via annulation reaction of α-halogenated N-acylhydrazones and isatin-derived MBH carbonates

• Xing Liu,
• Wenjing Shi,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2023, 19, 1923–1932, doi:10.3762/bjoc.19.143

• [indoline-3,5'-[1,2]diazepines] 3a–m were obtained in reasonable to good yields. Both, α-chloro- and α-bromo-N-acylhydrazones could be successfully used in the reaction and gave similar results. Also, hydrazones with different benzoyl-protecting groups were well tolerated in the reaction. In general, α

Trifluoromethylated hydrazones and acylhydrazones as potent nitrogen-containing fluorinated building blocks

• Zhang Dongxu

Beilstein J. Org. Chem. 2023, 19, 1741–1754, doi:10.3762/bjoc.19.127

• in various pharmaceutical and agrochemical products. This review focuses on the reactivity, synthesis, and applications of fluoromethylated hydrazones and acylhydrazones. It summarizes recent methodologies that have been used for the synthesis of various nitrogen-containing organofluorine compounds

• . Keywords: acylhydrazones; difluoromethylation; dihydropyridazine; fluorinated building blocks; hydrazones; imidazolidines; pyrazoles; pyrazolidines; pyrazolines; trifluoromethylation; Introduction The introduction of fluorine into pharmaceuticals, agrochemicals, and materials can significantly enhance

• building blocks offers another mainstream approach to introducing fluorine. Among these, di/trifluorodiazoethane [19][20][21][22], trifluoromethyl aldimines [23][24][25], trifluoroacetimidoyl halides [26], and fluoroalkyl N-sulfonyl hydrazones [27] have emerged as powerful nitrogen-containing fluorinated

Effects of the aldehyde-derived ring substituent on the properties of two new bioinspired trimethoxybenzoylhydrazones: methyl vs nitro groups

• Dayanne Martins,
• Roberta Lamosa,
• Talis Uelisson da Silva,
• Carolina B. P. Ligiero,
• Sérgio de Paula Machado,
• Daphne S. Cukierman and
• Nicolás A. Rey

Beilstein J. Org. Chem. 2023, 19, 1713–1727, doi:10.3762/bjoc.19.125

• studied and reported biological properties of this class [2][18][19][20]. Angelova and co-workers, for example, reported the ability of sulfonyl hydrazones and 4-methyl-1,2,3-thiadiazole-based hydrazone derivatives to inhibit the growth of several bacterial strains by interfering with their metabolism or

• cell membrane integrity [21]. In the context of cancer therapy development, metal complexes of N-acylhydrazones stand out. For example, Firmino et al. demonstrated that gallium(III) complexes of isoniazid-derived hydrazones exhibit strong cytotoxicity against HL-60 and HCT-116 cancer cell lines [22

• in AD. As a continuation of our long-term effort on the development of potentially bioactive N-acylhydrazones, the present work comprises a structural and spectroscopic comparison, from both experimental and theoretical viewpoints, of two structure-related hydrazones. Both compounds are new, and

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• , chalcogensuccinimide as an electrophile, and cyclopropane as a zwitterion component (Scheme 21) [58]. In 2020, a Lewis acid-mediated cyclization of β,γ-unsaturated oximes 51 and hydrazones 52 with N-(arylsulfenyl)succinimide 1 and N-(arylseleno)succinimide 1’’ was extended for the formation of isoxazoles 53 and

• construction of 4-chalcogenylated pyrazoles 57 and 59 was carried out starting from α,β-alkynic hydrazones 55 (Scheme 24) [60]. In the procedure, α,β-alkynic hydrazones were subjected to S- or Se-electrophiles 56 and cyclization reaction. Additionally, NCS and ArSH produced the S-electrophile for the

• cyclization reaction with arylpropynal hydrazones. Also, the reaction of 1-(1,3-diphenylprop-2-yn-1-ylidene)-2-phenylhydrazine 58 as the substrate with N-sulfenylsuccinimides 1 afforded fully substituted pyrazoles 59 in up to 98% yield. In 2021, a solvent-controllable approach for the construction of 3

Pyridine C(sp²)–H bond functionalization under transition-metal and rare earth metal catalysis

• Haritha Sindhe,
• Malladi Mounika Reddy,
• Karthikeyan Rajkumar,
• Akshay Kamble,
• Amardeep Singh,
• Anand Kumar and
• Satyasheel Sharma

Beilstein J. Org. Chem. 2023, 19, 820–863, doi:10.3762/bjoc.19.62

• significantly affect the C–H alkylation reaction and the reaction also proceeded well with hydrazones 13 obtained from aliphatic aldehydes or ketones. Based on mechanistic experiments and DFT calculations, the reaction presumably proceeds via a Cu–carbene migratory insertion (Scheme 4b). In the presence of CuI

Computational studies of Brønsted acid-catalyzed transannular cycloadditions of cycloalkenone hydrazones

• Manuel Pedrón,
• Jana Sendra,
• Irene Ginés,
• Tomás Tejero,
• Jose L. Vicario and
• Pedro Merino

Beilstein J. Org. Chem. 2023, 19, 477–486, doi:10.3762/bjoc.19.37

• Bilbao, Spain Instituto de Síntesis Química y Catálisis Homogénea (SQCH), Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain 10.3762/bjoc.19.37 Abstract The contribution to the energy barrier of a series of tethers in transannular cycloadditions of cycloalkenes with hydrazones has been computationally

• by the tethers, the entropy effects caused by them has also been studied. The analysis of the evolution of the electron localization function along the reaction revealed the highly concerted character of the reaction. Keywords: DFT; distortion model; hydrazones; transannular cycloadditions

• and co-workers demonstrated for transannular Diels–Alder cycloaddition reactions of symmetrically tethered large systems (10–18-membered rings) [29]. In this context, we have recently reported the transannular enantioselective (3 + 2) cycloaddition of cycloalkenone hydrazones under Brønsted acid

Inline purification in continuous flow synthesis – opportunities and challenges

• Jorge García-Lacuna and
• Marcus Baumann

Beilstein J. Org. Chem. 2022, 18, 1720–1740, doi:10.3762/bjoc.18.182

• evaporation, to waste, if it is the undesired phase, or to a further telescoped step. One example of this approach to separate hydrazones in dichloromethane after the aqueous quench is depicted in Scheme 6. This setup, although widely used in the above-mentioned group, has not been reported by other groups or

1,4,6,10-Tetraazaadamantanes (TAADs) with N-amino groups: synthesis and formation of boron chelates and host–guest complexes

• Artem N. Semakin,
• Ivan S. Golovanov,
• Yulia V. Nelyubina and
• Alexey Yu. Sukhorukov

Beilstein J. Org. Chem. 2022, 18, 1424–1434, doi:10.3762/bjoc.18.148

• hydrazone groups. The use of N-TAAD derivatives as potential ligands and receptors was showcased through forming boron chelates and host–guest complexes with water and simple alcohols. Keywords: azaadamantanes; cyclotrimerization; hydrazones; inclusion complexes; molecular recognition; Introduction

• cyclization of the corresponding tris-hydrazones, as well as the assembly of unsymmetrically substituted TAADs having both amino(amido) and hydroxy groups at bridge nitrogen atoms (2N,1O-TAADs and 1N,2O-TAADs) via a hitherto unknown co-trimerization of oxime and hydrazone units [35]. Also, structural studies

• -oxime form 1). Previous experimental and computational data evidence that cyclotrimerization of hydrazone groups proceeds more readily compared to oximes [18]. Hence, hydrazones 3 were expected to cyclize to corresponding TAADs 4 with high efficiency. On the other hand, cyclization of mixed oxime

Synthesis of N-phenyl- and N-thiazolyl-1H-indazoles by copper-catalyzed intramolecular N-arylation of ortho-chlorinated arylhydrazones

• Yara Cristina Marchioro Barbosa,
• Guilherme Caneppele Paveglio,
• Claudio Martin Pereira de Pereira,
• Sidnei Moura,
• Cristiane Storck Schwalm,
• Gleison Antonio Casagrande and
• Lucas Pizzuti

Beilstein J. Org. Chem. 2022, 18, 1079–1087, doi:10.3762/bjoc.18.110

• first reported synthesis of pharmacologically interesting N-thiazolyl derivatives. Keywords: fused-ring systems; hydrazones; indazoles; intramolecular cyclization; N-heterocycles; Introduction 1H-Indazoles are important scaffolds due to the prevalence in compounds with biological activity [1], such as

• reaction of hydrazones and p-benzoquinones [16], and Co3+/Cu2+-catalyzed C−N/N−N coupling of imidates with anthranils as both aminating reagents and organic oxidants [17]. Additional established routes to 1H-indazoles comprise transition metal‐catalyzed [18][19][20] and metal-free [21][22] intramolecular

• electrospray ionization (ESI) source (MicrOTOF-QII, Bruker Scientific) in positive mode. The compounds were individually dissolved in a solution of 50% chromatographic grade MeCN and 50% deionized H2O + 0.1% formic acid. General experimental procedure for the synthesis of hydrazones 1a–i In a 100 mL round

First series of N-alkylamino peptoid homooligomers: solution phase synthesis and conformational investigation

• Maxime Pypec,
• Laurent Jouffret,
• Claude Taillefumier and
• Olivier Roy

Beilstein J. Org. Chem. 2022, 18, 845–854, doi:10.3762/bjoc.18.85

• ]. In this seminal publication, hydrazones were utilized as submonomers in the displacement step of resin-bound bromoacetylated peptoids and cleavage from the resin with TFA containing 5% of triethylsilane resulted in a concomitant reduction of the imine functions in N-alkylamino groups. In this work

Flow synthesis of oxadiazoles coupled with sequential in-line extraction and chromatography

• Kian Donnelly and
• Marcus Baumann

Beilstein J. Org. Chem. 2022, 18, 232–239, doi:10.3762/bjoc.18.27

• -oxadiazole unit [28][29][30][31][32][33]. In 2012, Guin and co-workers described the iodine-mediated cyclodesulphurisation of thiosemicarbazides, yielding the corresponding 1,3,4-oxadiazoles [32]. Subsequently, Yu and co-workers reported the iodine-mediated oxidative cyclisation of acyl hydrazones to form

• biologically active reaction products, led us to explore the implementation of a continuous flow platform to reduce these hazards, while maintaining the high efficiency of the reaction. Results and Discussion We began with the investigation of various oxidative cyclisations of acyl hydrazones to compare the

• solubility only being observed in DMF and DMSO. Despite the slightly lower yield observed using DMF (entry 8, Table 2), it provided the option of a co-solvent system in situations where solubility in DMSO is insufficient. A variety of acyl hydrazones were subsequently synthesised from the corresponding

1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis

• Ruan Carlos B. Ribeiro,
• Patricia G. Ferreira,
• Amanda de A. Borges,
• Luana da S. M. Forezi,
• Fernando de Carvalho da Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5

• % yield (Scheme 11) [89]. Modifications in β-carbonyls 1,2-Naphthoquinone derivatives can be obtained through modifications in the carbonyls, leading to the formation of new compounds containing different groups, such as hydroxylamines, oxiranes, hydrazones, and heterocycles. These modifications can be

• synthesis of novel 4-amino-1,2-naphthoquinones 43a–c containing carbohydrates and evaluated their antitumor activity in vitro. These compounds were transformed into a series of hydrazones 44a–l with different substituted aryl groups, which were also evaluated against tumor cells. To prepare 43a–c, 18 was

• reacted with different amines 42a–c in the presence of an ethanol–water mixture under ultrasonication, followed by reaction with arylhydrazines, which led to hydrazones 44a–l according to the classical procedure that employs methanol at room temperature. All compounds were evaluated against different

Selective sulfonylation and isonitrilation of para-quinone methides employing TosMIC as a source of sulfonyl group or isonitrile group

• Chuanhua Qu,
• Run Huang,
• Yong Li,
• Tong Liu,
• Yuan Chen and
• Guiting Song

Beilstein J. Org. Chem. 2021, 17, 2822–2831, doi:10.3762/bjoc.17.193

• reductive strategy through nitrogen loss of sulfonyl hydrazones [13][14]. In addition, a sulfa-1,6-conjugated addition reaction [15][16][17] has also been developed for this purpose. Most of the reported methods are affected by long reaction times and the need for expensive metal catalysts or reagents

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• THF switched the product to thioketone 99 (Scheme 14). Refluxing the thioketones 99 again with phenylhydrazine hydrochloride in ethanol resulted in the desired bis(indol-3-yl)sulfides 98. On the other hand, the treatment of thioketones 99 with phenylhydrazine afforded the corresponding hydrazones 100