Mesoionic tetrazolium-5-aminides: Synthesis, molecular and crystal structures, UV–vis spectra, and DFT calculations

• Vladislav A. Budevich,
• Sergei V. Voitekhovich,
• Alexander V. Zuraev,
• Vadim E. Matulis,
• Vitaly E. Matulis,
• Alexander S. Lyakhov,
• Ludmila S. Ivashkevich and
• Oleg A. Ivashkevich

Beilstein J. Org. Chem. 2021, 17, 385–395, doi:10.3762/bjoc.17.34

• thermal stability of the tetrazolium-5-aminides (see Supporting Information File 1 for more details). Some nucleophilic displacement reactions were carried out in order to show the higher reactivity of the aminides in comparison to the parent aminotetrazoles. The high nucleophilicity of the imine group in

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• to give an imine in the first step, which is protonated by (S)-TRIP to generate the corresponding chiral CF3-substituted iminium ion. The latter subsequently reacts via the most accessible Re-face with indole 149 to afford the resulting Friedel–Crafts product 177. Worthy of note is the fact that the

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• imines 115, which led to alkylideneazetidines 116 (Scheme 52) [102]. The MgI2 acted as a Lewis acid and reducing agent, effecting the distal C–C bond cleavage in 113a to form an allenyl ketone, or an equivalent fluoro,iodo-enone species, either of which could then have added to the imine 115 and led to

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• hydride, known as Schwartz’s reagent [8]. This reduces the amide moiety, giving a complex that can be readily transformed into an imine or iminium cation [9]. It may perhaps be observed without straying too far afield from our primary focus that reduction of amides is actually not a leading use case of

• to the aforementioned method’s limitation to tertiary amides. Our previous work shows that Charette’s methodology is also not applicable in this case, as it does not lead to the formation of an imine [23]. Luckily, we were able to use a formerly established strategy based on Georg’s procedure with

• highest yield and diastereoselectivity, thus were chosen as optimal (Table 1, entry 9.). We also tried to isolate the imine after the reduction step and carry out the second step in a solvent commonly used for the Ugi–azide reaction alone. For this, we observed a significant decrease in overall yield and

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• synthesis of (±)-hirsutene (14) used an alkylidene carbene as source of TMM diyl in the intramolecular [3 + 2] cycloaddition [24] (Scheme 1D). Heating of epoxyaziridinyl imine 32 produced tricyclic compound 36 in 57% yield as a single product. The authors proposed that heating of epoxyaziridinyl imine 32

Ultrasound-assisted Strecker synthesis of novel 2-(hetero)aryl-2-(arylamino)acetonitrile derivatives

• Emese Gal,
• Luiza Gaina,
• Hermina Petkes,
• Alexandra Pop,
• Castelia Cristea,
• Gabriel Barta,
• Dan Cristian Vodnar and
• Luminiţa Silaghi-Dumitrescu

Beilstein J. Org. Chem. 2020, 16, 2929–2936, doi:10.3762/bjoc.16.242

• nucleophile to an imine C–N bond. Among the various cyanide transferring agents, which were largely documented in the search for advantageous synthetic procedures of these synthetic intermediates [17], trimethylsilyl cyanide (TMSCN) gave the possibility of accomplishing Strecker reactions using a wide variety

• (hetero)aromatic units and either electron-donating (methyl, methoxy) or electron-withdrawing groups (carboxy, nitro, etc.) pending on the imine substrate. The molecular structures of all synthesized α-(arylamino)acetonitriles 2a–j were fully characterized by spectroscopic methods. The MS spectra

Three-component reactions of aromatic amines, 1,3-dicarbonyl compounds, and α-bromoacetaldehyde acetal to access N-(hetero)aryl-4,5-unsubstituted pyrroles

• Wenbo Huang,
• Kaimei Wang,
• Ping Liu,
• Minghao Li,
• Shaoyong Ke and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2920–2928, doi:10.3762/bjoc.16.241

• proposed and is depicted in Scheme 5. Initially, a reaction of 1a and 3a occurred, providing an imine intermediate I, which tautomerized to the corresponding enamine form. Meanwhile, the activation of 2a with AlCl3 allowed the formation of a carbocation intermediate II, which was then trapped by the

• , affording the polysubstituted pyrazolo[3,4-b]pyridine 5a in 53% yield. The formation of an imine intermediate V may be involved in the reaction mechanism, and the enamine form of V contained two nucleophilic sites to react with a molecule of 3a, which generated the intermediate VI. Finally, VI underwent an

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

• Dmitrii A. Aksenov,
• Nikolai A. Arutiunov,
• Vladimir V. Maliuga,
• Alexander V. Aksenov and
• Michael Rubin

Beilstein J. Org. Chem. 2020, 16, 2903–2910, doi:10.3762/bjoc.16.239

• highly important imidazo[1,5-a]pyridines. It was imagined that the initial nucleophilic attack of the 2-(aminomethyl)pyridine (12) on the nitronate 2 would provide an amidinium species 13, which is very well suited for a 5-exo-trig cyclization involving the masked imine moiety of the pyridine ring

A heterobimetallic tetrahedron from a linear platinum(II)-bis(acetylide) metalloligand

• Matthias Hardy,
• Marianne Engeser and
• Arne Lützen

Beilstein J. Org. Chem. 2020, 16, 2701–2708, doi:10.3762/bjoc.16.220

• ligand syntheses is the subcomponent self-assembly strategy [18][19][20][21][22][23]. Following this strategy, the actual ligand is generated in situ during the self-assembly process via reversible formation of covalent bonds, in most cases imine bonds. Despite this achievement, addressing even higher

• (II) triflate hexahydrate in acetonitrile giving rise to the desired heterobimetallic [Fe4Pt6] complex as a mixture of diastereomers (Scheme 1). Despite the introduced imine functionalities, which are prone to hydrolysis, we did not observe any hydrolysis under the reaction conditions with at least 3

• equivalents of water per imine function that originate from the hydrate salt and imine condensations. Following this approach, the heterobimetallic cage 4 was obtained as a dark purple solid in 87% yield. Interestingly, complex 4 turned out to be rather stable as a solid under ambient conditions for several

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

• Alexander P. Molchanov,
• Mariia M. Efremova,
• Mariya A. Kryukova and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2020, 16, 2679–2686, doi:10.3762/bjoc.16.218

• cycloaddition of in situ-generated azomethine imine under microwave conditions is described. The reaction of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones proceeds regio- and stereoselectively giving mostly good yields of the corresponding perhydropyrazolopyrazoles. The products of the

• the hexahydropyrazolo[1,2-a]pyrazole ring, respectively, apparently through zwitterionic intermediates [28][29]. At the same time, the cycloaddition of azomethine imine to 1,3-diphenylprop-2-en-1-ones (chalcones) in IL proceeds stereo- and regioselectively giving two diastereomeric bicyclic anti

• formation of adduct 3m and pyrazoline 4b (Scheme 3). Thus, the azomethine imine A, formed by heating of DABCH 1a, either reacts with propenone 2f giving the adduct 3m or undergoes isomerization affording pyrazoline 4a. On the basis of this observation we suppose that the reaction products undergo

Asymmetric Mannich reactions of (S)-N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimines with yne nucleophiles

• Ziyi Li,
• Li Wang,
• Yunqi Huang,
• Haibo Mei,
• Hiroyuki Konno,
• Hiroki Moriwaki,
• Vadim A. Soloshonok and
• Jianlin Han

Beilstein J. Org. Chem. 2020, 16, 2671–2678, doi:10.3762/bjoc.16.217

• (Scheme 1b) [35]. Based on our experience in the preparation of trifluoromethylated amino compounds [36][37][38][39][40] and the chemistry of N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimine (1) [41][42][43][44][45][46][47][48][49][50][51][52][53][54], we noticed that the reactions of chiral imine 1 with

• mode of nucleophilic attack on the imine double bond in 1. As presented in Figure 3, imine 1 might react in the most stable conformation with the bulky tert-butyl group pointing away from the imine double bond. In this case the only stereocontrolling factor in play is the difference between the

• sulfinyl oxygen and the oxygen electron lone pair. The latter presents a lesser steric obstacle rendering the corresponding nucleophilic attack the more probable event. These ever-unexpected results strongly suggest that the origin of the stereocontrol in the reactions of imine 1 is not just the bulk of

Synthesis of novel fluorinated building blocks via halofluorination and related reactions

• Attila Márió Remete,
• Tamás T. Novák,
• Melinda Nonn,
• Matti Haukka,
• Ferenc Fülöp and
• Loránd Kiss

Beilstein J. Org. Chem. 2020, 16, 2562–2575, doi:10.3762/bjoc.16.208

• halolactons (rac)-17a,b. The initial attack of the halogen cation occurs at the sterically more accessible side of the C=C bond; (rac)-17a: X = Br; (rac)-2a: X = I. Unsuccessful halofluorination of the bicyclic diester 18. Halofluorination reactions of the rigid tricyclic imine 19. The relevant NOESY

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• then reduce 3-nitrobenzoic acid to the corresponding aniline 25 to turn over the cobalt cycle. Simultaneously, 23 condenses with the chiral primary amine catalyst 26 to give enamine intermediate 27, which can be intercepted by 24 to generate imine intermediate 28, which is finally hydrolysed to turn

• ketones 29 with 2-substituted indoles 30 as a precursor to imine 31, for the synthesis of indolin-3-ones 32 in good yields and excellent enantioselectivities (21 examples, up to >99:1 er) (Scheme 4a) [29]. Zhang et al. recently added to the scope of this family of reactions with their use of aldehydes

• -position of the iminium ion generating an unstable iminyl radical 52•+ that is quickly quenched by the nearby carbazole to form a more stable carbazole centred radical 53•+. Rapid tautomerisation to imine 54•+ precludes the undesired back electron transfer. Single electron reduction of 54•+ by PC•– and

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• worldwide. To this context, Hirao’s team has reported the synthesis of sumanenemonoone imine compounds 134 and 135 along with the Pd(II) complex 136 formed in a stepwise coordination manner investigated by a titration experiment (Scheme 35) [67]. As can be inspected from Scheme 35, compound 134 was prepared

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

• Yuqing Wang,
• Gaigai Wang,
• Anatoly A. Peshkov,
• Ruwei Yao,
• Muhammad Hasan,
• Manzoor Zaman,
• Chao Liu,
• Stepan Kashtanov,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2020, 16, 1963–1973, doi:10.3762/bjoc.16.163

• -component Passerini [19][20][21][22] and four-component Ugi [23][24] reactions that rely on the ability of organic isocyanides to participate in the nucleophilic attack onto the carbonyl or imine group are among the most studied MCRs. Accordingly, a wide range of post-MCR transformations have been

Natural dolomitic limestone-catalyzed synthesis of benzimidazoles, dihydropyrimidinones, and highly substituted pyridines under ultrasound irradiation

• Kumar Godugu,
• Venkata Divya Sri Yadala,
• Mohammad Khaja Mohinuddin Pinjari,
• Trivikram Reddy Gundala,
• Lakshmi Reddy Sanapareddy and
• Chinna Gangi Reddy Nallagondu

Beilstein J. Org. Chem. 2020, 16, 1881–1900, doi:10.3762/bjoc.16.156

• confirmed by 1H NMR spectral studies (Figure 7). In the 1H NMR spectrum (DMSO-d6), the two hydroxy protons of the bisimine I appeared as a broad, strongly downfield-shifted singlet at δ 13.19. The sharp singlet at δ 8.66 indicated the two imine protons (–N=CH) of the bisimine I. From this result, it was

• confirmed that the reaction stopped at the bisimine I stage. This was due to the intramolecular hydrogen bonding between the hydrogen atom of the ortho-hydroxy group and the nitrogen atom of the imine group in a six-membered ring transition state [87]. Similarly, the reaction between 3-ethoxysalicylaldehyde

Stereoselective Biginelli-like reaction catalyzed by a chiral phosphoric acid bearing two hydroxy groups

• Xiaoyun Hu,
• Jianxin Guo,
• Cui Wang,
• Rui Zhang and
• Victor Borovkov

Beilstein J. Org. Chem. 2020, 16, 1875–1880, doi:10.3762/bjoc.16.155

• proposed. As shown in Figure 1, the chiral phosphoric acid 3 activated the imine derivative, which in turn was formed by the condensation of benzaldehyde with N-benzylthiourea. The two hydroxy groups formed five-numbered intramolecular (blue dotted line) and seven-numbered intermolecular (red dotted lines

• ) H bondings with the enolizable ketone, respectively. This rigid chiral transition-state structure favored the stereoselective attack of the enol on the imine. Once the two hydroxy groups were etherified, the loss of the rigid structure would lead to low enantioselectivity. Additionally, this

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

• Dalel El-Marrouki,
• Sabrina Touchet,
• Abderrahmen Abdelli,
• Hédi M’Rabet,
• Mohamed Lotfi Efrit and
• Philippe C. Gros

Beilstein J. Org. Chem. 2020, 16, 1722–1731, doi:10.3762/bjoc.16.144

• . The reaction mechanism shown in Scheme 3 involves the formation of an imine upon the reaction of the primary amine with the most reactive carbonyl moiety (nonconjugated and exocyclic carbonyl function). Then, depending on the reaction conditions, the imine can react following a 1,2- or 1,4-addition

• of the intermediately formed imine to the Michael acceptor (Scheme 3). We then investigated the synthesis of cinnoline derivatives by mixing the diketone 5a and hydrazine monohydrate under various conditions (Table 2). We first investigated the reactivity in ethanol, as a protic solvent, at room

• leading to the formation of the indolone 7 starts with an imine formation between the secondary amine and the nonconjugated carbonyl from the 1,4-diketone. After an imine–enamine equilibrium, an intramolecular 1,4-addition to the Michael acceptor part of the molecule occurs, followed by a prototropy

Microwave-assisted efficient one-pot synthesis of N²-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

• Moustafa Sherief Moustafa,
• Ramadan Ahmed Mekheimer,
• Saleh Mohammed Al-Mousawi,
• Mohamed Abd-Elmonem,
• Hesham El-Zorba,
• Afaf Mohamed Abdel Hameed,
• Tahany Mahmoud Mohamed and
• Kamal Usef Sadek

Beilstein J. Org. Chem. 2020, 16, 1706–1712, doi:10.3762/bjoc.16.142

• attack of the primary amine in 7 to the same imine carbon produces the corresponding N2-(tetrazole-5-yl)-6-aryl-1,3,5-triazine-2,4-diamines 4 (route b). Alternatively, intermediate 8 could be obtained by a condensation of 5-aminotetrazole (3) with aromatic aldehydes 2 followed by the addition of

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• imine-derived CF3-containing enyne, bearing the trifluoromethylethynyl group at the ortho position (Scheme 16) [55]. One of the key steps in the preparation of the starting 1,n-enynes was a highly diastereoselective allylation reaction of chiral Ellman’s sulfinylimines. Based on this strategy, chiral

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

One-step route to tricyclic fused 1,2,3,4-tetrahydroisoquinoline systems via the Castagnoli–Cushman protocol

• Aleksandar Pashev,
• Nikola Burdzhiev and
• Elena Stanoeva

Beilstein J. Org. Chem. 2020, 16, 1456–1464, doi:10.3762/bjoc.16.121

• proposal features a stepwise Mannich-type reaction of the enolized anhydride 17 to the imine component and a subsequent N-acylation reaction to form the lactam target product [24]. A respective Mannich-type intermediate has been recently isolated and subsequently converted into the target lactam product

• [24]. It is also suggested that the imine substrate structure and the anhydride’s ability to undergo enolization have a profound influence on the reaction course [16][23]. While the reactions of homophthalic anhydride (10) and various cyclic imines 12 have been extensively explored [13][21][24][25

• temperature [32][33][34]. The anhydride was taken in slight molar excess in analogy to our previous work [21]. The reaction mixtures were heated for 6 h, until the imine 18 reacted completely. In the course of the reaction two stereocenters were formed at C-10b for 21 and C-11b for 22–24, respectively, and C

One-pot synthesis of 1,3,5-triazine-2,4-dithione derivatives via three-component reactions

• Gui-Feng Kang and
• Gang Zhang

Beilstein J. Org. Chem. 2020, 16, 1447–1455, doi:10.3762/bjoc.16.120

• involved in the methylation reaction mechanism (Scheme 5d). Based on previous literature reports and our experimental observations, a plausible mechanism for the synthesis of 6 is proposed in Scheme 6. Initially, the reversible nucleophilic attack of thiourea 2 on aldehyde 1 forms imine 8. Then, a

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

• Shrikant D. Tambe,
• Kwan Hong Min,
• Naeem Iqbal and
• Eun Jin Cho

Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114

• . The developed method can be employed for the synthesis of various bulky vicinal diamines, which are potential ligands in stereoselective synthesis. Keywords: 1,2-diamine; diversity; imine; photocatalysis; visible light; Introduction The selective formation of distinct valuable compounds from the

• of other valuable structural motifs via the careful control of the reaction conditions for the reaction of the biphenyl imine derivative N-benzylidene-[1,1'-biphenyl]-2-amine. Results and Discussion With the initial results in hand, we attempted the optimization of the reaction conditions to improve

• ] to the imine 1a, where the radical cation A donates a proton to 1a to form the α-amino radical intermediates B and C, which undergo cross-coupling to give the desired unsymmetrical vicinal diamine 2a. On the other hand, in CH3OH, 1a preferentially abstracts a proton from CH3OH rather than from A