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

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

• agrochemical industries. The (3 + 2)-cycloaddition between nitrile imines and alkenes represents one of the most efficient strategies to prepare these azacycles. However, conventional methods for the generation of the nitrile imine involved the use of unstable hydrazonoyl halides or the oxidation of aldehyde

• the electrogeneration of iodine in the aqueous phase. Under high stirring, the latter would react with NH-arylhydrazones 72 in the organic phase to furnish the N-iodo hydrazonium 75 and ultimately the nitrile imine 76 under basic conditions provided by the cathodic process. The critical role of the in

The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

• , was not observed. In 2016, Sashidhara et al. reported the catalytic effect of Ag(OTf) on GBB reactions, postulating its role in activating the attack of the isocyanides onto the imine intermediates [7]; some years later Liu et al. reported a similar role of AgOAc [8]. Although the reaction was tested

• significantly more active than 9, owing to higher rigidity and the correct position of the ortho H atoms in close proximity to the σ-holes on the I atom. The authors demonstrated that hydrogen bonding between H in ortho position of 8 and both O atom of aldehyde and N atom of imine significantly increased the

• its nucleophilicity and improving its orientation. Furthermore, Ser105 formed a strong hydrogen bond also with benzaldehyde, making it a better electron acceptor. Interestingly, also the imine intermediate showed strong interaction with Thr40 and Ser105 residues, so becoming a good electrophile for

Harnessing unprotected deactivated amines and arylglyoxals in the Ugi reaction for the synthesis of fused complex nitrogen heterocycles

• Javier Gómez-Ayuso,
• Pablo Pertejo,
• Tomás Hermosilla,
• Israel Carreira-Barral,
• Roberto Quesada and
• María García-Valverde

Beilstein J. Org. Chem. 2024, 20, 1758–1766, doi:10.3762/bjoc.20.154

• assayed in our group. Under these conditions, the bis-1,4-benzodiazepines 7 resulting from the reaction of the amino group with the imine on the benzodiazepine were obtained as a single diastereomer. On the basis of the preferred conformation for the 1,4-benzodiazepin-5-ones 5 and 6 [20][22], where the

Syntheses and medicinal chemistry of spiro heterocyclic steroids

• Laura L. Romero-Hernández,
• Ana Isabel Ahuja-Casarín,
• Penélope Merino-Montiel,
• Sara Montiel-Smith,
• José Luis Vega-Báez and
• Jesús Sandoval-Ramírez

Beilstein J. Org. Chem. 2024, 20, 1713–1745, doi:10.3762/bjoc.20.152

• C-3 or C-17 steroidal positions [49]. As an example, epi-androsterone was condensed with sulfanilamide resulting in the formation of substituted imine 90. Subsequent cycloaddition with thioglycolic acid under refluxing conditions in dioxane furnished the spiro N-aryl-1,3-thiazolidin-4-one 91. This

• -butylsulfinamide, leading to the formation of the imine 119. Subsequent reaction with allylmagnesium bromide yielded a mixture of 17-allyl 17-sulfonamido derivatives 120a,b in a 2.5:1 diastereomeric ratio (17S:17R), which were isolated and treated separately. Acid treatment of the sulfinamides 120a,b resulted in

• -II) afforded the corresponding 17-spirolactams 123a,b in 71–73% yield (Scheme 34). Notably, when (S)-(+)-tert-butylsulfinamide was used in the initial step of the reaction sequence, the allylation of the resulting imine proceeded diastereoselectively, yielding the 17-allyl-17-sulfinamido compound as

Methyltransferases from RiPP pathways: shaping the landscape of natural product chemistry

• Maria-Paula Schröder,
• Isabel P.-M. Pfeiffer and
• Silja Mordhorst

Beilstein J. Org. Chem. 2024, 20, 1652–1670, doi:10.3762/bjoc.20.147

• cyanoborohydride as a mild reducing agent, and paraformaldehyde as a methylating agent [36]. Methanol can be used as the methylating reagent in other methods. Here, a palladium on carbon (Pd/C) catalyst processes the dehydrogenation of the alcohol to form the corresponding aldehyde. The subsequently formed imine

Benzylic C(sp³)–H fluorination

• Alexander P. Atkins,
• Alice C. Dean and
• Alastair J. J. Lennox

Beilstein J. Org. Chem. 2024, 20, 1527–1547, doi:10.3762/bjoc.20.137

• secondary and tertiary substrates too. In 2012, Lectka reported a fluorination of mostly aliphatic C–H bonds that used a molecularly defined copper catalyst with a bis imine ligand, along with co-catalytic N-hydroxyphthalimide and a phase-transfer catalyst [51]. Although only a few benzylic substrates were

Synthesis of 2-benzyl N-substituted anilines via imine condensation–isoaromatization of (E)-2-arylidene-3-cyclohexenones and primary amines

• Lu Li,
• Na Li,
• Xiao-Tian Mo,
• Ming-Wei Yuan,
• Lin Jiang and
• Ming-Long Yuan

Beilstein J. Org. Chem. 2024, 20, 1468–1475, doi:10.3762/bjoc.20.130

• additive-free synthesis of 2-benzyl N-substituted anilines from (E)-2-arylidene-3-cyclohexenones and primary amines has been reported. The reaction proceeds smoothly through a sequential imine condensation–isoaromatization pathway, affording a series of synthetically useful aniline derivatives in

• acceptable to high yields. Mild reaction conditions, no requirement of metal catalysts, operational simplicity and the potential for scale-up production are some of the highlighted advantages of this transformation. Keywords: aniline; (E)-2-arylidene-3-cyclohexenone; imine condensation; isoaromatization

• -benzyl-N-substituted anilines. In this work, (E)-2-arylidene-3-cyclohexenones firstly react with primary amines to form cyclohexenylimine intermediates I. Afterward, isoaromatization resulting from imine–enamine tautomerization and exocyclic double bond shift occurs to give rise to stable aniline

Challenge N- versus O-six-membered annulation: FeCl₃-catalyzed synthesis of heterocyclic N,O-aminals

• Giacomo Mari,
• Lucia De Crescentini,
• Gianfranco Favi,
• Fabio Mantellini,
• Diego Olivieri and
• Stefania Santeusanio

Beilstein J. Org. Chem. 2024, 20, 1412–1420, doi:10.3762/bjoc.20.123

• Abstract A new class of heterocyclic N,O-aminal and hemiaminal scaffolds was successfully obtained by means of a three-component reaction (3-CR) of 1,2-diaza-1,3-dienes (DDs), α-aminoacetals and iso(thio)cyanates. These stable imine surrogates are generated from key-substituted (thio)hydantoin

• process and developed a catalytic system-controlled selective intramolecular N-annulation process for ring-fused biheterocyclic N,O-aminal derivatives as stable imine equivalents and useful tools for new bond formation in view of further fused-heterocylization processes. Moreover, control experiments

Domino reactions of chromones with activated carbonyl compounds

• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 1256–1269, doi:10.3762/bjoc.20.108

• intermediate AE. Attack of the imine to the carbonyl group and subsequent extrusion of water afforded product 40. The reaction proved to be rather general and a variety of substituted 3-cyanochromones were successfully employed. 1,3-Bis(silyloxy)-1,3-butadienes The two-step reaction of 3-cyanochromones 16a–h

Bismuth(III) triflate: an economical and environmentally friendly catalyst for the Nazarov reaction

• Manoel T. Rodrigues Jr.,
• Aline S. B. de Oliveira,
• Ralph C. Gomes,
• Amanda Soares Hirata,
• Lucas A. Zeoly,
• Hugo Santos,
• João Arantes,
• Catarina Sofia Mateus Reis-Silva,
• João Agostinho Machado-Neto,
• Leticia Veras Costa-Lotufo and
• Fernando Coelho

Beilstein J. Org. Chem. 2024, 20, 1167–1178, doi:10.3762/bjoc.20.99

• synthesis has been reported for several transformations, such as epoxide opening [56], ketal formation and deprotection [57][58], Mannich reaction [59], intramolecular Sakurai cyclization [60], alcohol oxidation [61], aromatic hydrocarbon nitration [62], imine allylation [63], Knoevenagel condensation [64

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

• aldehydes or ketones, undergo base-assisted condensation reactions with amines providing the corresponding imines. In the last step, the active manganese hydride complexes reduce the imine compounds and afford the desired alkylated amine products (Scheme 2B). Several well-defined manganese complexes have

• synthesis of amines and imines using Mn-pincer catalyst [37]. When t-BuOK (1 equiv) was used as a base, alkylated amine products were observed selectively using alcohol as an alkylating agent, whereas when t-BuONa (1.5 equiv) was used as base, alkylated imine products were isolated (Scheme 6). This

• then undergo condensation with formaldehyde providing an N-phenylmethanimine intermediate which was confirmed by 1H NMR spectroscopy. In the final step, the imine undergoes hydrogenation with Mn3-b to yield the N-methylated product (Scheme 16). In 2020, Maji et al. synthesized manganese(I) complexes

Light on the sustainable preparation of aryl-cored dibromides

• Fabrizio Roncaglia,
• Alberto Ughetti,
• Nicola Porcelli,
• Biagio Anderlini,
• Andrea Severini and
• Luca Rigamonti

Beilstein J. Org. Chem. 2024, 20, 1076–1087, doi:10.3762/bjoc.20.95

• context of covalent organic frameworks (COFs) and metal-organic frameworks (MOFs), frequently assembled through imine linkages. While C–H activation through halogens presents clear technical advantages, it also brings forth concerns about the toxicity of halo compounds to both human health and the

(Bio)isosteres of ortho- and meta-substituted benzenes

• H. Erik Diepers and
• Johannes C. L. Walker

Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78

• substituted ortho-benzene. Stephenson and co-workers accessed 1,2-BCHeps 79a–c by insertion of alkenes into BCPs 78, and proposed the 1,2-BCHeps as isosteres of ortho-benzenes (Scheme 7A) [46]. The reaction proceeded via homolytic cleavage of a C–C bond adjacent to the imine functionality and stepwise alkene

Activity assays of NnlA homologs suggest the natural product N-nitroglycine is degraded by diverse bacteria

• Kara A. Strickland,
• Brenda Martinez Rodriguez,
• Ashley A. Holland,
• Shelby Wagner,
• Michelle Luna-Alva,
• David E. Graham and
• Jonathan D. Caranto

Beilstein J. Org. Chem. 2024, 20, 830–840, doi:10.3762/bjoc.20.75

• , Supporting Information File 1). Notably, the YjgF protein previously proposed to aid in deamination of imines – a proposed direct product of NNG degradation by NnlA – is absent [20]. This observation suggests this protein is not needed to aid in glyoxylate formation. Therefore, imine hydrolysis to glyoxylate

• may occur non-enzymatically or is catalyzed within the NnlA active site. However, an imine product has not yet been observed and further investigations of the NNG degradation mechanism are needed. Given the potential widespread presence of NnlA, it is possible that NnlA could mediate previously

HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

• Luan A. Martinho and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2024, 20, 628–637, doi:10.3762/bjoc.20.55

• reactivity of the imine formation [24]. The most common catalysts are those derived from triflate salts such as Sc(OTf)3 [25], Yb(OTf)3 [26], In(OTf)3 [27] and Gd(OTf)3 [28], and inorganic Brønsted or Lewis acids like HClO4 [29], ZrCl4 [30], InCl3 [31], BiCl3 [32], RuCl3 [33], NH4Cl [34], HCl [35], LaCl3

• ethanol was not observed. 2-Aminopyridines containing a chlorine atom in positions 4 or 5 provided the products 4mm–uu in excellent yields (up to 97%). Nonetheless, with 2-amino-3-bromopyridine, low product yields were observed for 4vv–xx, which may be due to the high hindrance of that substrate to imine

A laterally-fused N-heterocyclic carbene framework from polysubstituted aminoimidazo[5,1-b]oxazol-6-ium salts

• Andrew D. Gillie,
• Matthew G. Wakeling,
• Bethan L. Greene,
• Louise Male and
• Paul W. Davies

Beilstein J. Org. Chem. 2024, 20, 621–627, doi:10.3762/bjoc.20.54

• type (Scheme 1a, path a). However, attempts to form the desired imidazolium ring from 3 using triethyl orthoformate and different additives were unsuccessful. Similarly, an imine precursor 6, prepared in high yields by synthesising the known acetal-bearing oxazole 5 [21] and reacting it with 2,6

• introduce a formamide motif in place of the amine or imine to allow the use of more forcing cyclisation conditions (Scheme 1a, path c). Oxazole 8a was obtained in good yield from 1a using only a slight excess of nitrenoid 7 and 2 mol % catalyst loading. Heating 8a in the presence of POCl3 afforded the 3

Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

• bisalkynylplatinum(II)–terpyridine clips [54]. The dimer showed photocatalytic activity in the photooxidation of a secondary amine to the corresponding imine that could be deactivated and reactivated by opening or closing the tweezers. Variations on multidentate N-donor ligands have also been developed by Lehn and

Facile approach to N,O,S-heteropentacycles via condensation of sterically crowded 3H-phenoxazin-3-one with ortho-substituted anilines

• Eugeny Ivakhnenko,
• Vasily Malay,
• Pavel Knyazev,
• Nikita Merezhko,
• Nadezhda Makarova,
• Oleg Demidov,
• Gennady Borodkin,
• Andrey Starikov and
• Vladimir Minkin

Beilstein J. Org. Chem. 2024, 20, 336–345, doi:10.3762/bjoc.20.34

• amines, the direction of which is controlled by the large positive charge at the C(2) center of the p-quinone imine moiety of the heterocycle. With this in mind, we turned our attention to solid-state organic reactions. Numerous examples of nucleophilic substitutions at carbon centers are discussed in

• condensation of 3H-phenoxazin-3-one (1) with various o-aminophenols (in refluxing DMF for 8–10 h), upon formation of the corresponding imine intermediate, affords benzo[5,6][1,4]oxazino[2,3-b]phenoxazines derivatives 10a,b (triphenodioxazines). As shown in the present work, this reaction can also be performed

• absorption spectral data are given in Table 3. Conclusion The diverse reactions of 3H-phenoxazin-3-one derivatives with nucleophilic reagents are primarily directed toward the p-quinone imine fragment [5][13][15]. In the presence of protonic acids, the reaction with amines proceeds through Schiff base

Substituent-controlled construction of A₄B₂-hexaphyrins and A₃B-porphyrins: a mechanistic evaluation

• Seda Cinar,
• Dilek Isik Tasgin and
• Canan Unaleroglu

Beilstein J. Org. Chem. 2023, 19, 1832–1840, doi:10.3762/bjoc.19.135

• -porphyrins concomitantly formed in yields between 9–17%. When p-methoxy- and p-hydroxy-substituted N-tosylimines 2h and 2i were used in this reaction, substrate 2h gave only the A3B-porphyrin while the imine 2i did not form any product (Table 1, entries 8 and 9). To further evaluate the scope of the reaction

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

• . Hydrazones can be regarded as electrophilic and nucleophilic imine equivalents, and thus they represent valuable and versatile building blocks in synthetic chemistry [32][33][34][35][36]. Trifluoroacetaldehyde hydrazones can be regarded as an equivalent of fluorine-containing azomethine imines in the

• trifluoroacetonitrile imine, are highly versatile in that they react with olefins, acetylenes, dimethyl fumarate, dimethyl maleate, β-diketones, β-keto esters, bicyclic olefins, and potassium isothiocyanate and isocyanate affording the corresponding trifluoromethyl-containing compounds, generally with good yields [51

• regioselective [3 + 2] cycloadditions [59][60][61][62][63] (Scheme 10a). Similarly, trifluoroacetonitrile imine reacted with mercaptoacetaldehyde and mercaptocarboxylic acids to generate fluorinated 1,3,4-thiadiazines with good yields via a [3 + 3] annulation [64] (Scheme 10b). Meanwhile, mercaptoacetaldehyde as

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

• ability to undergo E/Z isomerization in a stimuli-responsive imine bond is what makes this class useful for applications in the field of molecular electronics, as switchers [5][6]. In addition, these compounds can also adopt syn- or antiperiplanar conformations, due to the constriction of the rotation

Tying a knot between crown ethers and porphyrins

• Maksym Matviyishyn and
• Bartosz Szyszko

Beilstein J. Org. Chem. 2023, 19, 1630–1650, doi:10.3762/bjoc.19.120

• other two have imine character [11][12]. They are rigid, planar molecules which feature macrocyclic aromaticity due to the cyclic delocalisation of π electrons [13]. The well-defined macrocyclic cavity termed the coordination core, can encompass one, two, or more central ions (typically metal/metalloid

• of the research on crowned porphyrins, the Bowman-James group worked on developing a new type of porphyrinoids called accordion porphyrins. Their seminal contribution, published in 1984, demonstrated a facile synthesis of an imine-linked tetrapyrrole macrocycle in the presence of a metal template and

• laid the ground for a whole new research area of hybrid imine-porphyrinoids [52][53][54]. Bowman-James' work provided an exciting insight into accordion porphyrins' coordination chemistry, demonstrating the tremendous potential of iminoporphyrinoids as macrocyclic ligands. Independently the Sessler

Unravelling a trichloroacetic acid-catalyzed cascade access to benzo[f]chromeno[2,3-h]quinoxalinoporphyrins

• Chandra Sekhar Tekuri,
• Pargat Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2023, 19, 1216–1224, doi:10.3762/bjoc.19.89

• beginning of the reaction, copper(II) 2,3-diamino-5,10,15,20-tetraarylporphyrins 1 react with 2-hydroxynaphthalene-1,4-dione (2) in the presence of trichloroacetic acid to form an imine intermediate which on intramolecular cyclization affords a key benzo[f]quinoxalinoporphyrin intermediate 17. Further, a

Synthesis of tetrahydrofuro[3,2-c]pyridines via Pictet–Spengler reaction

• Elena Y. Mendogralo and
• Maxim G. Uchuskin

Beilstein J. Org. Chem. 2023, 19, 991–997, doi:10.3762/bjoc.19.74

• -c]pyridines. From the analysis of the literature data [2][40][41][42][43], we suggested that the interaction of furanic amines with various aldehydes in an acidic media should be accompanied by the formation of the corresponding imine, the generation of the iminium cation, and subsequent Pictet

• the results of our study of this tandem reaction. Results and Discussion Initially, we synthesized the key imine 3a by refluxing a solution of the starting 2-(5-methylfuran-2-yl)ethylamine (1a) and commercially available benzaldehyde (2a) in absolute CH3CN for one hour in a quantitative yield. To our

• delight, when 2 equiv of HCl were subsequently added to the solution of imine 3a at 50 °C, the formation of the desired 2-methyl-4-phenyl-4,5,6,7-tetrahydrofuro[3,2-c]pyridine (4a) was observed in 26% yield (Table 1, entry 1). It should be noted that most part of the product 4a was formed as the