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

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• properties, and chemical reactivity between oxime radicals and other types of N-oxyl radicals. For a long time, the synthetic potential of iminoxyl radicals remained underestimated and their chemistry was mainly represented by fundamental physico-chemical studies. The precursors of imine-N-oxyl radicals are

• of N-benzylidenemethylamine (40), shows the dependence of the imine yield on reaction time and temperature (Scheme 13). Higher yields of 40 were achieved at lower temperatures but longer reaction times were necessary in this case [85]. Di-tert-butyliminoxyl radicals react with Grignard reagents and

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• radical adds to the imine substrate 5.5, yielding the desired amine product 5.6. Finally, the same group developed a photochemical radical alkylation of heteroarenes with alkyl trifluoroborate salts (Scheme 6) [51]. In this reaction, the photoinduced oxidative fragmentation of the alkyl trifluoroborate

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• -[18F]fluorophenylalanines 72a,b [54] were achieved by a copper-mediated nucleophilic radiofluorination of arylstannanes 71a,b with [18F]KF (Scheme 17). 1.6. Alkylation of benzophenone imine of glycine ester Pentafluoro-ʟ-phenylalanine (77a) and 2,4-ditrifluoromethyl-ʟ-phenylalanine (77b) were

• synthesized through alkylation of the benzophenone imine of glycine ester 73, with perfluorinated benzylbromide 19c or 2,4-bis(trifluoromethyl)benzyl bromide (74) in the presence of 2,7-bis[O(9)-allylhydrocinchonidinium-N-methyl]naphthalene dibromide, to afford the fluorinated phenylalanine imines 75a,b with

• ] (Scheme 41). An alternative approach to the difluorinated compound 168a was achieved by the condensation of 164a with (S)-1-phenylethylamine (169), to give the imine 170. Heating of imine 170 with TMSCN in the presence of zinc iodide [82] generated the nitrile 171 as a 1:1 mixture of diastereoisomers

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• superoxide radical anion oxidizes the alcohol to aldehyde, which is then converted to an imine after coupling with the amine. The products are obtained after cyclization and oxidation of the cyclic intermediates (Scheme 21) [46]. Similarly, Jiang and co-workers reported the selective photooxidation of

• ion, then giving an imine after deprotonation (Scheme 50). Adopting this strategy, Che and co-workers obtained several imines in 90–99% yield from secondary amines [102] (Scheme 51). The authors observed that the oxidation is regioselective, occurring at the less substituted position of nonsymmetric

• ) due to the low reversibility of the double bond formation. Initially, the photocatalytic oxidative amine coupling was selected as a reaction model [103]. The authors observed that the imine-based Por-COF-1, decomposed completely, and no target product was detected. Nevertheless, the Por-COF-2

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• discussed in the literature whether metal cations are coordinated in a monodentate fashion to the phenolate oxygen atom or rather in a bidentate fashion both to the phenolate oxygen and the imine nitrogen atoms of the open merocyanine form [25][28]. Furthermore, density functional theory (DFT) calculations

• styrylquinolinizium unit at the neighboring carbon atom C5’’. At the same time, imine groups also have a high binding affinity to Cu2+ [83][84][85] and Fe3+ [86][87] so that we propose the initial coordination of the metal cation mainly to the imine nitrogen atom of the spirooxazine group in the course of the

• upon the addition of Hg2+ may have been caused by the low propensity of these cations to coordinate to the imine functionality and/or the inability to be involved in the subsequent electron transfer. Conclusion The spirooxazine–quinolizinium conjugates 3a and 3b were synthesized by a base-catalyzed

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• , to the amide 83, as shown in Scheme 22. The low yield of the amide formation was attributed mainly to a concurrent imine formation, which was catalyzed by benzoic acid formed as a result of benzaldehyde (8) oxidation during the photoreaction. There was also a competition between two bimolecular

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• with Suginome’s PhMe2Si-BPin [35] as a silicon pro-nucleophile (Scheme 11A) [36]. The mechanism followed the expected pathway involving transmetallation from boron to copper to form the corresponding Cu–Si species III. This intermediate then adds to the imine 45 to give intermediate IV, which after

•  46). The product featuring the PhMe2Si residue at the β-location 287, however, arises by way of a 1,2-addition to an imine, formed from the same Pd(II) intermediate via elimination [84]. Oestrich and co-workers have recently demonstrated non-directed, asymmetric syn-addition-silylations of 3,3

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• -functionalized nanosilica. Finally, the complexation reaction of Cu(II) with a supported ligand on propylamine-functionalized nanosilica, 10, was performed to produce a Cu(II) benzimidazole–salen complex supported by imine-functionalized silica (BS–Cu(II)@SiO2 (11), Scheme 2). The nanocatalyst 11 was used to

• carboxaldehyde was reacted with 3-aminopropyl-functionalized SBA-15 in dry ethanol at 60 °C for one day to afford the SBA-15-supported imine ligand 69 (Scheme 12) [35]. The solid product was filtered off, washed with toluene/ethanol, and dried. The SBA-15-supported imine composite was added to an ethanolic

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• nitriles [21], carbonyl or imine species [22], iodonium or diazonium salts [23], or halide species [24]. The formation of radicals from halide species by photoredox catalysis has been widely studied. It has been applied as a mild method for the dehalogenation of several compounds [25][26][27]. In the light

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• pyridylphosphine ligands. Synthesis of triazolylphosphine ligands. Ferrocenyl pyridylphosphine imine ligands. Synthesis of phosphinooxazolines (PHOX). Synthesis of ferrocenylphosphine oxazoles. Selected works on the applications of P,N-phosphine ligands. Funding The authors acknowledge University of KwaZulu-Natal

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• derivatives were prepared upon the reaction of the corresponding oximes with isocyanates. These novel compounds reacted photochemically in the presence of supercoiled plasmid DNA. Structure–activity relationship (SAR) studies revealed that the substituent on the imine group was not affecting the extend of the

• carbamates [61][64][65] where 1H NMR spectroscopy has been used in order to distinguish between the two [61][65]. Thus, the imine benzylic proton of the E-stereoisomers shows a singlet in the area 8–8.7 ppm, whereas the ones belonging to a Z-conformation are upfield and appear between 7.3–7.6 ppm. Indeed

• state of 12 is transferred to CR and DNA is not damaged (well 10). Conclusion p-Pyridyl oxime carbamates bearing electron-donating or electron-withdrawing substituents on the aromatic carbamate group and an amine, a methyl or a hydrogen on the imine moiety, were successfully synthesized in high yields

Rapid, two-pot procedure for the synthesis of dihydropyridinones; total synthesis of aza-goniothalamin

• Thomas J. Cogswell,
• Craig S. Donald and
• Rodolfo Marquez

Beilstein J. Org. Chem. 2020, 16, 135–139, doi:10.3762/bjoc.16.15

• , acrylamide was used in an analogous manner to the carbamates employed by Veenstra (Scheme 1) [19]. In our initial attempts, the solvent was changed from dichloromethane to acetonitrile due to solubility issues with the acrylamide and the postulated imine intermediate. The reaction proved sluggish, taking

• four days to reach completion; however, the dialkene 5 was isolated in a very encouraging 66% yield (Scheme 2). In an attempt to increase the yield of the overall process, the reaction conditions were optimized to reach complete formation of imine 6, before treatment with allyltrimethylsilane to

• consistently high results over the 2-pot process, producing dihydropyridinones 9a and 9c–e in high yields. The electron-withdrawing substituted aromatic starting materials on the other hand, gave a low yield in the first step, which we believe was due to poor solubility of the imine intermediate. In contrast

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• molecule of ethyl cyanoacetate (4) attacks the alkynone 3a in a Michael addition. A second molecule 4 then attacks the cyano substituent and an imine is formed. The ester substituent of the initially reacted more electrophilic ethyl cyanoacetate (4) is presumably cleaved by a base-mediated acyl cleavage

Unexpected one-pot formation of the 1H-6a,8a-epiminotricyclopenta[a,c,e][8]annulene system from cyclopentanone, ammonia and dimethyl fumarate. Synthesis of highly strained polycyclic nitroxide and EPR study

• Sergey A. Dobrynin,
• Igor A. Kirilyuk,
• Yuri V. Gatilov,
• Andrey A. Kuzhelev,
• Olesya A. Krumkacheva,
• Matvey V. Fedin,
• Michael K. Bowman and
• Elena G. Bagryanskaya

Beilstein J. Org. Chem. 2019, 15, 2664–2670, doi:10.3762/bjoc.15.259

• heterocycle formation [11]. Presumably, a prototropic shift in the enamine-imine intermediate 4 is followed by electrocyclization to the cyclic azomethine ylide, which then reacts with dimethyl fumarate in a 1,3-dipolar cycloaddition. The suggested mechanism accounts for the trans-position of the methyne

A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light

• Xavier Gómez-Santacana,
• Sabrina M. de Munnik,
• Tamara A. M. Mocking,
• Niels J. Hauwert,
• Shanliang Sun,
• Prashanna Vijayachandran,
• Iwan J. P. de Esch,
• Henry F. Vischer,
• Maikel Wijtmans and
• Rob Leurs

Beilstein J. Org. Chem. 2019, 15, 2509–2523, doi:10.3762/bjoc.15.244

• . proceeding through a tert-butylimine intermediate (31) formed under Dean–Stark conditions [32]. This imine was reacted with NaOiPr to form the ether 32, which was subsequently hydrolyzed to obtain the desired aldehyde 28g in high yield. Reductive amination of the aldehydes 28f–h with 7 furnished amines 16f–h

Sugar-derived oxazolone pseudotetrapeptide as γ-turn inducer and anion-selective transporter

• Sachin S. Burade,
• Sushil V. Pawar,
• Tanmoy Saha,
• Navanath Kumbhar,
• Amol S. Kotmale,
• Manzoor Ahmad,
• Pinaki Talukdar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2019, 15, 2419–2427, doi:10.3762/bjoc.15.234

• showed a broad band at 3444–3421 cm−1 indicating the presence of -NHs of amine/amide functionalities. The bands at 1740 and 1688 cm−1 were assigned to the lactone carbonyl and amide (as well as imine) groups, respectively. In the 1H NMR spectrum, the downfield signals at δ 9.03 and 8.52 ppm were assigned

• signal at δ 163.0 ppm was assigned to the -C=N functionality. The 1H,15N-HSQC and 1H,15N-HMBC spectra showed a signal at δ 246.0 ppm that was assigned to the imine (C=N-) nitrogen. The signal at δ 26.2 ppm was assigned to the amine (NH2) nitrogen. The signals at δ 112.8 and δ 114.1 ppm were due to the

• δ 2.0 ppm, integrating for three protons, was assigned to the NHCOCH3. In the 13C NMR spectrum, the appearance of five signals in the downfield region (at δ 171.6, 170.9, 167.5, 165.0, and 164.0 ppm) indicated the presence of three amides, lactone carbonyl and imine carbon (-C=N) suggesting the

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• one case, phenol PEG (poly(ethylene glycol) was grafted together with pyridine imine phenol, affording dendrimers stochastically functionalized on the surface, but all having precisely 12 fluorophores in the internal structure [59]. Another way to induce solubility in water consists in having

• at different time points after spinal cord injury. This dendrimer has potential uses as a drug/siRNA carrier and phenotype-specific cell tracer, i.e., for enhanced cell therapies combined with monitoring of cell fate and function [61]. Dendrimers with pyridine imine terminal functions and their

• copper complexes have an interesting antiproliferative capacity towards a range of human cancer cell lines, inducing early apoptosis, followed by secondary necrosis [64]. The fluorescent analog having pyridine imine and PEG terminal functions shown in Scheme 7 has been synthesized with the aim of

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• boronic acid had been widely utilized to disconnect the N–O bond as well as to hydrolyze the resulting imine into a ketone [52]. We applied this method to deprotect the isoxazoline 3. However, the desired β-hydroxy ketone was never obtained. In one instance, the methyl ketone from a retro-aldol reaction

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• for the aziridine ring opening and the removal of the 1-phenylethyl group and also for the reduction of the intermediate cyclic imine which appeared stereospecific. Two other piperidine alkaloids, (+)-deoxocassine ((2S,3S,6R)-190a) and (+)-spectaline ((2S,3S,6R)-190b) were synthesized as hydrochloride

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• addition with a subsequent intramolecular cyclization catalyzed by Cu(BDC)MOF. Further, the LC–MS study of the reaction mixture has shown the imine formation to be the major pathway rather than β-nitrostyrene. The reaction involved a two-step reaction mechanism in which aza-Michael adduct 13 was formed in

• the formation of radical intermediates, as use of TEMPO inhibited intramolecular C(sp3)–H amination of imine species. Aerial oxidation of the Cu(I) species bonded to the N-atom of pyridine and imine 39 resulted in Cu(II) superoxo radical intermediate 40. This was followed by intramolecular hydrogen

• sodium ascorbate (NaOAs) helped in the reduction of Cu(II) to Cu(I) which then reacted with the alkyne moiety. The species thus formed participated in the reaction by reacting with imine of aldehyde and amidine. The intermediate thus formed undergo 5-exo-dig cyclization and 1,3-H shift to form the final

Synthesis of ([1,2,4]triazolo[4,3-a]pyridin-3-ylmethyl)phosphonates and their benzo derivatives via 5-exo-dig cyclization

• Aleksandr S. Krylov,
• Artem A. Petrosian,
• Julia L. Piterskaya,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2019, 15, 1563–1568, doi:10.3762/bjoc.15.159

• nucleophilic substitution of chlorine in the chloroethynylphosphonate to form ynamine intermediate A, isomerization of which provides ketenimine B. Further formation of the imine tautomer C enables an intramolecular 5-exo-dig cyclization to furnish the title [1,2,4]triazolo[4,3-a]pyridines (Scheme 6

Synthesis of pyrrolo[1,2-a]quinolines by formal 1,3-dipolar cycloaddition reactions of quinolinium salts

• Anthony Choi,
• Rebecca M. Morley and
• Iain Coldham

Beilstein J. Org. Chem. 2019, 15, 1480–1484, doi:10.3762/bjoc.15.149

• ylide, or by condensation of a primary amine with an aldehyde to give an imine followed by prototropy or deprotonation to give N-metalated azomethine ylides (see, for example, [5][6][7][8][9][10][11][12][13][14][15][16][17][18]). An alternative method is to prepare a salt of a heterocycle, typically by

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• materials for relevant MCRs such as those based on imine and isocyanide. The focus is mainly posed on proving the amenability of MCRs for the diversity-oriented derivatization of naturally occurring steroids and the construction of complex steroid-based platforms for drug discovery, chemical biology and

• first step of the Ugi-4CR reaction, i.e., the formation of the imine between the ketosteroid and the amine group of the aminopyridine derivative. Then, the imine suffers the nucleophilic attack of the isocyanide generating a nitrilium intermediate. Differently from the Ugi-4CR, the final step is the

• cyclization between the pyridine N atom and the isocyanide. TP3 plays the catalytic role by acidic activation of the ketone to favor the imine formation. 2.1.2 Steroids as amine and carboxylic acid components: Several groups have employed steroidal substrates as amino and carboxylic acid components of the Ugi

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• through an addition of copper acetylide, generated from terminal alkyne and copper, to the imine formed by the reaction between the amine and the formyl group. Then, the secondary propargylamine intermediate would act as a nucleophile in a cyclization process to form the lactam ring. The same

• became predominant. Similarly to the above mentioned method, the first step in this approach is probably the imine formation by reaction of amine 2 with the aldehyde functionality of benzoate 29. Next, addition of the enol form of ketone 31 onto the imine would provide a Mannich intermediate amine, which

• start with the formation of an imine intermediate between the aldehyde function of 33 and the amine 2, followed by a nucleophilic attack by the diketone and a final intramolecular cyclization, the Han group proposes a different pathway, with an initial deprotonation of ketoacid 34 (R2 = Me, Ar, R3 = OH