Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[c]quinolizinium ions

• Julika Schlosser,
• Olga Fedorova,
• Yuri Fedorov and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 101–117, doi:10.3762/bjoc.20.11

• species (ROS), such peroxyl, alkoxy and hydroxyl radicals, or carbon-centered radicals, which subsequently induce DNA strand cleavage. In the type-II mechanism, a triplet-excited photosensitizer reacts with molecular oxygen to give highly reactive singlet oxygen, 1O2, as reactive intermediate, which in

• hydroxyl radicals [79] or interfere with the DNA damage by alternative pathways [80]. In any case, the significant decrease of DNA damage in the presence of the radical scavengers indicated the formation and direct or indirect participation of carbon radicals and hydroxyl radicals in the photoinduced DNA

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations

• Laura Abella,
• Gerard Novell-Leruth,
• Josep M. Ricart,
• Josep M. Poblet and
• Antonio Rodríguez-Fortea

Beilstein J. Org. Chem. 2024, 20, 92–100, doi:10.3762/bjoc.20.10

• molecules on surfaces like graphene or carbon nanotubes have allowed the scientific community to visualize at atomic resolution the structural changes of molecules in situ by single-molecule atomic-resolution real-time TEM imaging (SMART-TEM) [1][2][3][4][5]. Since the initial discovery [2], many movies

• have been published that record the dynamic behavior of a wide range of molecules and chemical reactions. One such process was the dimerization of C60 fullerene in a carbon nanotube peapod, i.e., hybrid structures consisting of fullerene molecules encapsulated in single-walled carbon nanotubes (SWCNT

• analyzed the interaction between C60 and the nanotube within the peapod. Next, we have found that some dimeric C60–C60 fullerene structures inside the carbon nanotube are thermodynamically favorable. Experiments indicate that, besides C60 sensitization via a singlet excited state, the [2 + 2] cycloaddition

Optimizing reaction conditions for the light-driven hydrogen evolution in a loop photoreactor

• Pengcheng Li,
• Daniel Kowalczyk,
• Johannes Liessem,
• Mohamed M. Elnagar,
• Dariusz Mitoraj,
• Radim Beranek and
• Dirk Ziegenbalg

Beilstein J. Org. Chem. 2024, 20, 74–91, doi:10.3762/bjoc.20.9

• , Germany 10.3762/bjoc.20.9 Abstract Photocatalytic hydrogen production from water is a promising way to fulfill energy demands and attain carbon emission reduction goals effectively. In this study, a loop photoreactor with a total volume of around 500 mL is presented for the photocatalytic hydrogen

• evolution using a Pt-loaded polymeric carbon nitride photocatalyst under 365 nm irradiation in the presence of sacrificial reducing agents. The fluid flow pattern of the developed photoreactor was characterized experimentally and the photon flux incident to the loop photoreactor was measured by chemical

• be applied. Notably, the loop photoreactor demonstrated an external photon efficiency up to 17 times higher than reported in literature studies, while scaling the reactor size by a factor of 10. Keywords: loop photoreactor; parametric study; photocatalytic hydrogen evolution; polymeric carbon

Multi-redox indenofluorene chromophores incorporating dithiafulvene donor and ene/enediyne acceptor units

• Christina Schøttler,
• Kasper Lund-Rasmussen,
• Line Broløs,
• Philip Vinterberg,
• Ema Bazikova,
• Viktor B. R. Pedersen and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2024, 20, 59–73, doi:10.3762/bjoc.20.8

• expanded by pyrrolo annelation. The optical and redox properties of these compounds, in some cases carbon-rich, were studied by UV–vis absorption spectroscopy and cyclic voltammetry. Synthetically, the work explores IF diones or fluorenone as central building blocks by subjecting the carbonyl groups to a

• -olefinations, and Knoevenagel condensations. In particular, the acetylenic scaffolds presented in this work may be useful precursors for even more elaborate, conjugated and carbon-rich structures in future work. Experimental Anhydrous MeOH was obtained by distillation from activated Mg and stored over 3 Å

• platinum disk (diameter = 1.6 mm) or a glassy carbon disk (3 mm) was used as the working electrode. The reference electrode was separated from the solution containing the substrate by a ceramic frit. Measured potentials were referenced to ferrocene/ferrocenium (Fc/Fc+) redox couple, measured before and

Preparing a liquid crystalline dispersion of carbon nanotubes with high aspect ratio

• Keiko Kojima,
• Nodoka Kosugi,
• Hirokuni Jintoku,
• Kazufumi Kobashi and
• Toshiya Okazaki

Beilstein J. Org. Chem. 2024, 20, 52–58, doi:10.3762/bjoc.20.7

• Keiko Kojima Nodoka Kosugi Hirokuni Jintoku Kazufumi Kobashi Toshiya Okazaki Nano Carbon Device Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan Department of Chemistry, University of Tsukuba, 1-1-1 Tennodai, Tsukuba

• 305-8571, Japan 10.3762/bjoc.20.7 Abstract We successfully prepared a surfactant-assisted carbon nanotube (CNT) liquid crystal (LC) dispersion with double-walled CNTs (DWCNTs) having a high aspect ratio (≈1378). Compared to dispersions of single-walled CNTs (SWCNTs) with lower aspect ratio, the

• . Keywords: aqueous dispersion; bar-coating; carbon nanotube; coffee-ring effect; liquid crystal; Introduction Carbon nanotubes (CNTs) are cylindrical carbon structures with high electrical conductivity and tensile strength in the direction of the tube, anticipated as durable and highly conductive fibers

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions

• Matthias R. Steiner,
• Max Schmallegger,
• Larissa Donner,
• Johann A. Hlina,
• Christoph Marschner,
• Judith Baumgartner and
• Christian Slugovc

Beilstein J. Org. Chem. 2024, 20, 41–51, doi:10.3762/bjoc.20.6

• similar phosphonium salt 2,4-di-tert-butyl-6-(triphenylphosphonium)phenolate features this particular signal at 6.27 ppm (4JHH = 2.7 Hz, 3JPH = 14.4 Hz [30]). In the 13C NMR spectra, the chemical shifts of the carbon atoms in positions 1 and 6 of the phenolate unit are particularly noteworthy. In the

• adducts 2a–i, the carbon atom 1, featuring the phenolate oxygen atom attached, shows a doublet (2JPC ≈ 4 Hz) in the range of 175.0–173.9 ppm (Table 1). In the closely related 2,4-di-tert-butyl-6-(triphenylphosphonium)phenolate the chemical shift for the corresponding carbon atom appears at 173.8 ppm (2JPC

• about 150 ppm [36]. The opposite is true for the resonance of the carbon atom 6 having the phosphonium center attached, which is distinctly more shielded in 2a–i (96.9–95.3 ppm, 1JPC ≈ 100 Hz) then in 1 (119.9 ppm, 1JPC = not observed) [35]. Likewise, the two ipso-carbons of the phenyl groups attached

Facile access to pyridinium-based bent aromatic amphiphiles: nonionic surface modification of nanocarbons in water

• Lorenzo Catti,
• Shinji Aoyama and
• Michito Yoshizawa

Beilstein J. Org. Chem. 2024, 20, 32–40, doi:10.3762/bjoc.20.5

• )2–Y (Y = OCH3, OH, and imidazole)). The new amphiphiles quantitatively self-assemble into ≈2 nm-sized aromatic micelles in water independent of the side-chain. Importantly, efficient water-solubilization and nonionic surface modification of various nanocarbons (e.g., fullerene C60, carbon nanotubes

• ., graphitic carbon nitride) in the form of 10–30 nm-sized stacks is also demonstrated using the present amphiphiles. Keywords: aromatic micelle; nanocarbon; nonionic surface modification; pyridinium; water-solubilization; Introduction Nanocarbons, such as fullerenes, graphenes, and carbon nanotubes, are

• of the side-chain present. Importantly, efficient water-solubilization and nonionic surface modification of nanocarbons (i.e., fullerene C60 (C60), single/multi-walled carbon nanotubes (s/m-CNT), and graphene nanoplatelets (GN)) can be achieved through noncovalent encircling with the present

Cycloaddition reactions of heterocyclic azides with 2-cyanoacetamidines as a new route to C,N-diheteroarylcarbamidines

• Pavel S. Silaichev,
• Tetyana V. Beryozkina,
• Vsevolod V. Melekhin,
• Valeriy O. Filimonov,
• Andrey N. Maslivets,
• Vladimir G. Ilkin,
• Wim Dehaen and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2024, 20, 17–24, doi:10.3762/bjoc.20.3

• -atoms atoms bound to carbon were placed in the calculated positions and were refined in isotropic approximation. The hydrogen atoms of NH2 groups were refined independently with isotropic displacement parameters. The solution and refinement of the structures were accomplished with the Olex2 program

Synthesis of N-acyl carbazoles, phenoxazines and acridines from cyclic diaryliodonium salts

• Nils Clamor,
• Mattis Damrath,
• Thomas J. Kuczmera,
• Daniel Duvinage and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2024, 20, 12–16, doi:10.3762/bjoc.20.2

• mol % raised yields to synthetically useful 74% (Table 1, entry 7). The excess amount of 1a was still necessary as a significant amount of iodobiphenyl is formed under the reaction conditions as a result of an undesired heterolytic iodine–carbon bond cleavage. Other carbonate bases and changing the Cu

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF₃: the case of alkyne hydration. Chemistry vs electrochemistry

• Marta David,
• Elisa Galli,
• Richard C. D. Brown,
• Marta Feroci,
• Fabrizio Vetica and
• Martina Bortolami

Beilstein J. Org. Chem. 2023, 19, 1966–1981, doi:10.3762/bjoc.19.147

• analysis (amidine carbon atom at 161.6 ppm in BMIm-BF4, taking as internal reference the imidazolium C2 at 136.4 ppm) [116]. The addition of an excess of BF3·Et2O to the solution of DBU in IL shifted the DBU amidine signal to 166.0 ppm, confirming the rapid formation of the adduct (see Supporting

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

• Nedra Touj,
• François Mazars,
• Guillermo Zaragoza and
• Lionel Delaude

Beilstein J. Org. Chem. 2023, 19, 1947–1956, doi:10.3762/bjoc.19.145

• cyclic (alkyl)(amino) or mesoionic carbenes (CAACs or MICs) onto carbon disulfide. Nine novel compounds were isolated and fully characterized by 1H and 13C NMR, FTIR, and HRMS techniques. Moreover, the molecular structures of two CAAC·CS2 and two MIC·CS2 betaines were determined by X-ray diffraction

• heterocycles; zwitterions; Introduction Following the seminal discovery from the group of Arduengo, who isolated and fully characterized 1,3-di(1-adamantyl)imidazol-2-ylidene in 1991 [1], stable divalent carbon species have evolved from fleeting intermediates to ubiquitous catalysts, ligands, and reagents in

• of charges (Figure 1) [13][14][15][16]. Crabtree and co-workers first reported the abnormal binding of an imidazolium salt to an iridium hydride at the C4 carbon atom instead of C2 in 2001 [17][18]. Since then, many other metal complexes bearing imidazol-4-ylidene ligands (F) have been reported [7

Studying specificity in protein–glycosaminoglycan recognition with umbrella sampling

• Mateusz Marcisz,
• Sebastian Anila,
• Margrethe Gaardløs,
• Martin Zacharias and
• Sergey A. Samsonov

Beilstein J. Org. Chem. 2023, 19, 1933–1946, doi:10.3762/bjoc.19.144

• distance) is very similar to the widely used RMSD but instead of using specific atoms it compares atom types (e.g., any carbon atom to any carbon atom instead of specifically numbered carbon atom to the carbon atom with the same number). RMSatd is more appropriate when used for long and periodic molecules

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

• depicted in Scheme 5. At first, MBH carbonates of isatin 2 is attacked at the α-position by the Lewis base to give the ammonium salt A with elimination of carbon dioxide and a tert-butoxide ion. Secondly, the ammonium salt A is deprotonated by the in situ generated tert-butoxide ion to give the allylic

Beyond n-dopants for organic semiconductors: use of bibenzo[d]imidazoles in UV-promoted dehalogenation reactions of organic halides

• Kan Tang,
• Megan R. Brown,
• Chad Risko,
• Melissa K. Gish,
• Garry Rumbles,
• Phuc H. Pham,
• Oana R. Luca,
• Stephen Barlow and
• Seth R. Marder

Beilstein J. Org. Chem. 2023, 19, 1912–1922, doi:10.3762/bjoc.19.142

• ; reduction; reductive dimerization; Introduction Reductive dehalogenation reactions of organic halides can be used in organic synthesis as a means of generating carbon-centered radical or anion intermediates and could have relevance to the treatment of waste halogenated polymers. While such reactions can be

Biphenylene-containing polycyclic conjugated compounds

• Cagatay Dengiz

Beilstein J. Org. Chem. 2023, 19, 1895–1911, doi:10.3762/bjoc.19.141

• ; biphenylene; [N]phenylenes; polycyclic aromatic compounds; Introduction Acenes represent an important category of carbon-rich polycyclic aromatic hydrocarbons (PAHs) characterized by the presence of linearly fused benzene rings [1][2]. Investigating the electronic properties of acenes is essential for

• understanding the correlations between structure and electronic properties, as these units serve as fundamental building blocks in graphite and carbon nanotubes [3]. The limited stability of this particular class of PAHs arises as a key challenge, primarily attributed to their extended conjugation. The longer

Anion–π catalysis on carbon allotropes

• M. Ángeles Gutiérrez López,
• Mei-Ling Tan,
• Giacomo Renno,
• Augustina Jozeliūnaitė,
• J. Jonathan Nué-Martinez,
• Javier Lopez-Andarias,
• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2023, 19, 1881–1894, doi:10.3762/bjoc.19.140

• , stands for the stabilization of anionic transition states on π-acidic aromatic surfaces. Anion–π catalysis on carbon allotropes is particularly attractive because high polarizability promises access to really strong anion–π interactions. With these expectations, anion–π catalysis on fullerenes has been

• introduced in 2017, followed by carbon nanotubes in 2019. Consistent with expectations from theory, anion–π catalysis on carbon allotropes generally increases with polarizability. Realized examples reach from enolate addition chemistry to asymmetric Diels–Alder reactions and autocatalytic ether cyclizations

• . Currently, anion–π catalysis on carbon allotropes gains momentum because the combination with electric-field-assisted catalysis promises transformative impact on organic synthesis. Keywords: anion–π interactions; autocatalysis; catalysis; carbon nanotubes; Diels–Alder reactions; electric-field-induced

Aromatic systems with two and three pyridine-2,6-dicarbazolyl-3,5-dicarbonitrile fragments as electron-transporting organic semiconductors exhibiting long-lived emissions

• Karolis Leitonas,
• Brigita Vigante,
• Dmytro Volyniuk,
• Audrius Bucinskas,
• Pavels Dimitrijevs,
• Sindija Lapcinska,
• Pavel Arsenyan and
• Juozas Vidas Grazulevicius

Beilstein J. Org. Chem. 2023, 19, 1867–1880, doi:10.3762/bjoc.19.139

• × ttr), where d represents the thickness of the organic layer, and U corresponds to the applied voltage over the sample. Cyclic voltammetry (CV) measurements were conducted using a mAUTOLAB type III galvanostat, employing a glassy carbon working electrode in a three-electrode cell configuration. The

Controlling the reactivity of La@C₈₂ by reduction: reaction of the La@C₈₂ anion with alkyl halide with high regioselectivity

• Yutaka Maeda,
• Saeka Akita,
• Mitsuaki Suzuki,
• Michio Yamada,
• Takeshi Akasaka,
• Kaoru Kobayashi and
• Shigeru Nagase

Beilstein J. Org. Chem. 2023, 19, 1858–1866, doi:10.3762/bjoc.19.138

• , the third carbon allotrope, have unique spherical molecular structures and exhibit high reactivity as electron-deficient polyolefins. The excellent redox properties of fullerenes are useful for their chemical derivatization and practical applications [1][2][3][4][5]. Fullerene anions can be easily

• @C2v-C82(CHClC6H3Cl2) [19] and La@C2v-C82(CBr(CO2Et)2) [23], by single-crystal X-ray diffraction (SC-XRD) analysis. Based on the similarity in the absorption spectra of La@C2v-C82(CHClC6H3Cl2), the addition site of 3a–c was expected to be at the C10 (for the numbering of carbon atoms in La@C2v-C82; see

• ) values [26] of the carbon atoms (θσπ-90˚) of the La@C2v-C82 anion were calculated using density functional theory (DFT) [27][28][29][30][31][32][33]. As shown in Table 1 and Figure 6, the C1, C2, and C3 atoms have large negative charge densities (C1: −0.1498, C2: −0.1828, C3: −0.1126), and C1 and C2

A novel recyclable organocatalyst for the gram-scale enantioselective synthesis of (S)-baclofen

• Gyula Dargó,
• Dóra Erdélyi,
• Balázs Molnár,
• Péter Kisszékelyi,
• Zsófia Garádi and
• József Kupai

Beilstein J. Org. Chem. 2023, 19, 1811–1824, doi:10.3762/bjoc.19.133

• reaction could be used in the synthesis of several drugs to form a carbon–carbon bond in a stereoselective manner [6][35]. Our goal was to synthesize the chiral precursor 17 of baclofen (Scheme 3). To achieve this objective, we first planned to use Meldrum’s acid and 4-chloro-trans-β-nitrostyrene (16

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• ), specifically by extracting a hydrogen atom from the α-position of benzyl radicals A. The process described above led to the formation of the corresponding olefins 11, eliminating the need for a carbon–iodine bond formation step. Alkylation Diaziridines are highly versatile building blocks in synthesis, with

• emphasized their significance in facilitating the synthesis of diverse compounds and paving the way for further advancements in the field of photocatalysis. The highly efficient construction of carbon–heteroatom (C–X) bonds is of significant importance in the fields of natural products, pharmaceuticals, and

• -unsaturated phthalimide 33a. Simultaneously, radical III of the catalyst was also formed, accompanied by the extrusion of CO2. Subsequently, the alkyl radical A added to the carbon–carbon triple bond of enynal 32g, resulting in the formation of a vinyl radical intermediate B, followed by a 5-exo-trig

Selectivity control towards CO versus H₂ for photo-driven CO₂ reduction with a novel Co(II) catalyst

• Lisa-Lou Gracia,
• Philip Henkel,
• Olaf Fuhr and
• Claudia Bizzarri

Beilstein J. Org. Chem. 2023, 19, 1766–1775, doi:10.3762/bjoc.19.129

• Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany 10.3762/bjoc.19.129 Abstract Developing efficient catalysts for reducing carbon dioxide, a highly stable combustion waste product, is a relevant task to lower the atmospheric

• selectivity from 6% to 97% after four hours of irradiation at 420 nm. Further efficiency enhancement was achieved by adding 1,1,1,3,3,3-hexafluoropropan-2-ol, producing CO with a TON up to 230, although at the expense of selectivity (54%). Keywords: carbon monoxide selectivity; cobalt(II) complex; copper(I

• photosynthesis. Taking Nature as a model, the absorption of photons can drive electron-transfer processes, leading to the production of highly energetic molecules. By aiming at the conversion of CO2, a greenhouse gas implicated in climate change, the closure of the carbon cycle can be achieved [2]. For this

Unprecedented synthesis of a 14-membered hexaazamacrocycle

• Anastasia A. Fesenko and
• Anatoly D. Shutalev

Beilstein J. Org. Chem. 2023, 19, 1728–1740, doi:10.3762/bjoc.19.126

• = 11.2 Hz), four NH2 groups at 6.27, 5.72, 5.59, and 4.61 ppm (singlets). Signals of 11 different carbon atoms including 8 carbons of two methylpyrazole moieties were observed in the 13С NMR spectrum. Thus, we concluded that the impurity has bis-pyrazole structure 6. This structure was also confirmed by

• the 1H,13C-HSQC and 1H,13C-HMBС spectra, as well as by comparing the experimental carbon chemical shifts in DMSO-d6 with those calculated for 6 by the GIAO method at the PBE1PBE/6-311+G(2d,p) level of theory using the DFT B3LYP/6-311++G(d,p) optimized geometries (DMSO solution) and applying a multi

• the 1H and 13C{1H} NMR spectra of compound 5 in DMSO-d6 show only a half-number set of proton or carbon signals (five and six signals, respectively), thus indicating its C2-symmetric dimeric structure. The analysis of 2D NMR spectroscopic data provided additional evidence for the macrocycle 5

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

• of compounds is also related to the ability of N-acylhydrazones to exist as different isomers and/or tautomers. They can exist as geometric isomers (E/Z), which differ in the orientation of the groups around the carbon–nitrogen double bond [2][3], as well as amido and iminol tautomers [4]. The

• -substituent in the aldehyde-derived portion of hdz-NO2 caused a strong deshielding of the hydroxy group (assigned at 12.84 ppm) due to the removal of electron density on the carbon adjacent to –OH. On the other hand, in hdz-CH3, the presence of the methyl substituent moderately shields this proton (11.89 ppm

• relative to the azomethine group as the intramolecular H-bond between the phenolic hydrogen and double-bonded nitrogen activates the azomethine carbon for a nucleophilic attack by a solvent molecule, an important step in the development of a new bioactive hydrazonic derivative is the assessment of its

Quinoxaline derivatives as attractive electron-transporting materials

• Zeeshan Abid,
• Liaqat Ali,
• Sughra Gulzar,
• Faiza Wahad,
• Raja Shahid Ashraf and
• Christian B. Nielsen

Beilstein J. Org. Chem. 2023, 19, 1694–1712, doi:10.3762/bjoc.19.124

• Organic semiconductors have emerged as a fascinating class of materials with significant implications for numerous scientific disciplines, including electronics, photonics, and energy conversion. These materials, composed of carbon-based molecules or polymers, offer remarkable flexibility, tunability, and

Decarboxylative 1,3-dipolar cycloaddition of amino acids for the synthesis of heterocyclic compounds

• Xiaofeng Zhang,
• Xiaoming Ma and
• Wei Zhang

Beilstein J. Org. Chem. 2023, 19, 1677–1693, doi:10.3762/bjoc.19.123

• classified as stabilized (A1–A4) which contain an electron-withdrawing group (EWG), semi-stabilized (B1–B4) which have an aryl (Ar) substituent, and non-stabilized (C1 and C2) which have neither an Ar group nor an EWG on the α-carbon atoms. The routes to access AMYs of different classes are shown in Scheme 1

• anionic charge on the α-carbon connecting to the EWG. They are popular AMYs for 1,3-diploar [3 + 2] cycloaddition reactions with alkenes to generate pyrrolidines 1a–d with high regio- and stereoselectivities. They have been reported in a huge number (1,000+) of publications [18][19][20][21][22][23][24][25

• ][26][27][28]. It is worth noting that among the products 1a–d, only compound 1d has hydrogen atoms on both the nitrogen and α-carbon atoms, which makes it suitable to be used for a second cycloaddition to form double [3 + 2] cycloaddition products 2 [29][30]. The N–R-type AMYs B1 and B2 bearing an Ar