(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

Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

• Anup Biswas

Beilstein J. Org. Chem. 2023, 19, 956–981, doi:10.3762/bjoc.19.72

• with the elimination of a H+ ion to form the functionalized aromatic moieties. The aza-Friedel–Crafts reaction is a subclass of the originally reported transformation that couples an imine with an aromatic system allowing for a facile incorporation of an alkylamine functionality into the aromatic

• lone pair of electrons of the imine nitrogen to a suitable vacant orbital of the metal center, thus enhancing the electrophilicity of the imine carbon atom by imparting a positive character on the adjacent heteroatom [22][23]. With the advent of different types of organocatalysts, the aza-Friedel

• –Crafts reaction has also been explored under the influence of organocatalysis. However, here organocatalysts act as Brønsted acids which form noncovalent interactions (H-bonding) with the imine nitrogen to enhance the electrophilicity of the imine component. In addition, by selecting suitable imine

Clauson–Kaas pyrrole synthesis using diverse catalysts: a transition from conventional to greener approach

• Dileep Kumar Singh and
• Rajesh Kumar

Beilstein J. Org. Chem. 2023, 19, 928–955, doi:10.3762/bjoc.19.71

• shown in Scheme 20b. In this mechanism, calcium nitrate first activates the decomposition process of 2,5-DMTHF (2) from A to B. Further, a nucleophilic attack of amines 42 on B generates imine intermediate C. Finally, intramolecular nucleophilic attack by enamine D on the aldehyde group, dehydration and

Synthesis of aliphatic nitriles from cyclobutanone oxime mediated by sulfuryl fluoride (SO₂F₂)

• Xian-Lin Chen and
• Hua-Li Qin

Beilstein J. Org. Chem. 2023, 19, 901–908, doi:10.3762/bjoc.19.68

• afford the iminyl radical intermediate II. In the following step, the ring-strain of cyclobutanone is released under the promotion of the imine radical, giving the C-centered radical III which is subsequently captured by the alkene. Meanwhile, the radical IV transfers an electron to [Cun+1] regenerating

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

• involves the formation of (dibenzylamido)yttrium complex 28 by the reaction of yttrium complex 26 with HNBn2. Then σ-bond metathesis between the Y–N bond of 28 and the ortho-C–H bond of pyridine gives η2-pyridyl species 29 which on imine insertion produces species 30. Subsequent protonation then provides

• yields generating a library of isonicotinic and nicotinic acid derivatives. Another inexpensive and non-toxic iron-catalyzed C–H arylation of pyridines has been reported by DeBeof and co-workers [98]. Using the imine in 147 as directing group, afforded the arylated pyridine products 150 in good to high

• reaction conditions. Also, the additive KF was employed in order to minimize the oxidative iron-catalyzed homocoupling of 148. An imine directing group at the para-position in pyridine 147 lead to activated ortho-position products 150 within 15 minutes. The imine group of the products can further be

Eschenmoser coupling reactions starting from primary thioamides. When do they work and when not?

• Lukáš Marek,
• Jiří Váňa,
• Jan Svoboda and
• Jiří Hanusek

Beilstein J. Org. Chem. 2023, 19, 808–819, doi:10.3762/bjoc.19.61

• . recommended [24] a polar aprotic solvent such as DMSO that facilitates the formation of both α-thioiminium salt (III) as well as Eschenmoser contraction involving the attack of the exposed carbanion towards the imine/iminium group (V). Based on our previous experience [3][4] we favor dimethylformamide (DMF

• ) level of theory. Quantum calculations (Figure 2) have shown that the reaction pathway that involves an intramolecular proton transfer between the α-carbon and imine nitrogen through TS1 is much more favorable for imidothioate derived from 4-bromoisoquinoline-1,3(2H,4H)-dione (3) and 3-bromooxindole (1

Sulfate radical anion-induced benzylic oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines

• Joydev K. Laha,
• Pankaj Gupta and
• Amitava Hazra

Beilstein J. Org. Chem. 2023, 19, 771–777, doi:10.3762/bjoc.19.57

• single electron transfer (SET), is proposed to be involved in the plausible reaction mechanism. Keywords: arylsulfonylimine; benzylic oxidation; benzyl sulfonamide; K2S2O8; sulfate radical anion; Introduction Among various imine compounds [1], N-arylsulfonylimines are perhaps the most prominent due to

• of the intermediate product 2c and 2-aminobenzamide gave 2-(p-tolyl)quinazolin-4(3H)-one (4b) in 85% yield. Furthermore, when various other ortho-substituted aniline derivatives such as 2-aminobenzylamine, 2-aminothiophenol, and o-phenylenediamine are reacted with imine 2a in a similar manner, the

• abstracts the activated NH proton to produce imine 2. The dual role of SO4·− involving HAT and SET is proposed in this plausible mechanism, which requires further investigation. Similarly, a plausible mechanism for the one-pot synthesis of N-heterocycles is shown in Scheme 6. Initially, the N

Construction of hexabenzocoronene-based chiral nanographenes

• Ranran Li,
• Di Wang,
• Shengtao Li and
• Peng An

Beilstein J. Org. Chem. 2023, 19, 736–751, doi:10.3762/bjoc.19.54

• through oxidative cyclodehydrogenation and imine formation in a 72% yield. It was noted that no other regioisomer was detected for the asymmetrical precursor 30. The pair of enantiomers was confirmed by the racemic structure's single-crystal X-ray diffractometry and separated by chiral HPLC, and no

Palladium-catalyzed enantioselective three-component synthesis of α-arylglycine derivatives from glyoxylic acid, sulfonamides and aryltrifluoroborates

• Bastian Jakob,
• Nico Schneider,
• Luca Gengenbach and
• Georg Manolikakes

Beilstein J. Org. Chem. 2023, 19, 719–726, doi:10.3762/bjoc.19.52

• imine species provide a very flexible approach to the arylglycine scaffold [2][9]. The Petasis borono-Mannich reaction constitutes a prominent example for such an imine-based multicomponent reaction (Scheme 1a). The reaction of glyoxylic acid, an amine component and an arylboronic acid offers a highly

• situ generation of reactive imine species, we have disclosed iron- and bismuth-catalyzed three-component reactions for the synthesis of α-arylglycines [14][15][16], in which the arylboronic acid could be replaced with an electron-rich (hetero)arene as nucleophile. In parallel, we have developed

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• been shown to impart high levels of enantioselectivity for these ketones [46]. We performed the conjugate addition for 2 h and then added imine 58 having a tosyl protecting group. The workup allowed the isolation of domino products 59 as a mixture of diastereomers with dr 3:2 and enantiomeric purities

• introduced during the conjugate addition). On the other hand, a typical problem of these reactions was also revealed. The diastereoselectivity with respect to the addition to the imine was only very modest. To address the problem of low facial selectivity of the imine addition, we continued our study with

• ligands is that they can also promote the conjugate additions of aryl-based or branched Grignard reagents (Scheme 17) [49]. Further extending this methodology, we have investigated formaldehyde imine equivalents. These kinds of imines are not readily available, but they are highly important synthetic

C3-Alkylation of furfural derivatives by continuous flow homogeneous catalysis

• Grédy Kiala Kinkutu,
• Catherine Louis,
• Myriam Roy,
• Juliette Blanchard and
• Julie Oble

Beilstein J. Org. Chem. 2023, 19, 582–592, doi:10.3762/bjoc.19.43

• .19.43 Abstract The C3-functionalization of furfural using homogeneous ruthenium catalysts requires the preinstallation of an ortho-directing imine group, as well as high temperatures, which did not allow scaling up, at least under batch conditions. In order to design a safer process, we set out to

• formation of the imine directing group and the C3-functionalization with some vinylsilanes and norbonene. Keywords: biomass; C–H activation; flow; furfural; homogeneous catalysis; Introduction The conversion of biomass derivatives into value-added products is one of the key branches of green chemistry and

• reaction conditions while providing products in shorter reaction times. In addition, the ability to couple multiple reactors with a flow apparatus could also enable us to perform these functionalizations directly from furfural by forming the imine in a first reactor. It should be noted that, in batch, in

A new oxidatively stable ligand for the chiral functionalization of amino acids in Ni(II)–Schiff base complexes

• Alena V. Dmitrieva,
• Oleg A. Levitskiy,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2023, 19, 566–574, doi:10.3762/bjoc.19.41

• reversibility can be reached at scan rates above 20 V/s allowing the E1/2 estimation. Similarly to previously studied complex (ΔAlaNi)L1 [36], electron transfer to (ΔAlaNi)L7 is mainly ligand centered. The DFT-estimated LUMO is formed as an overlap of the π antibonding orbitals of the dehydroalanine and imine

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• occurs producing 144. Subsequently, coordination of the Rh(I) to the electrophilic cyano group leads to an intramolecular addition producing 145. The imine undergoes a hydrolysis releasing the final carboannulated product 141 as well as regeneration of the active Rh(I) catalyst. A similar mechanism can

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

• )) geometries for the transition structures of series a–f. Top: Cycloaddition of protonated hydrazones as inverse-demand reaction of cycloaddition of azomethine imines. Bottom: molecular orbitals involved in the reaction and energy diagram of the reactivity of ethylene with azomethine imine and protonated