Mechanochemical halogenation of unsymmetrically substituted azobenzenes

• Dajana Barišić,
• Mario Pajić,
• Ivan Halasz,
• Darko Babić and
• Manda Ćurić

Beilstein J. Org. Chem. 2022, 18, 680–687, doi:10.3762/bjoc.18.69

• reaction dynamics and characterization of the products was achieved by in situ Raman and ex situ NMR spectroscopy and PXRD analysis. A strong influence of the different 4,4’-substituents of azobenzene on the halogenation time and mechanism was found. Keywords: azo compounds; halogenation; mechanochemistry

Tuning the solid-state emission of liquid crystalline nitro-cyanostilbene by halogen bonding

• Subrata Nath,
• Alexander Kappelt,
• Matthias Spengler,
• Bibhisan Roy,
• Jens Voskuhl and
• Michael Giese

Beilstein J. Org. Chem. 2021, 17, 124–131, doi:10.3762/bjoc.17.13

• , enantiotropic phase transitions were observed exclusively for NO2-C10∙∙∙F4Az, indicating a different solid-state arrangement of the azo compounds compared to the stilbazole-based assemblies. The mesomorphic properties of all nitro compounds and the assemblies are summarised in Figure 3 and Table 1. The strength

• induction of liquid crystallinity in our assemblies, we synthesised a series of azo compounds with decreasing fluorination degree at the halogen bond donating iodobenzene [12]. Reducing the number of the fluorine atoms at the halogen bond donating moiety lowers the polarisation of the iodine atom and thus

• segments, which is crucial for the formation of a mesophase [7][20]. The azo compounds with a weakly polarised iodine atom (F2Az or F2’Az) have significantly lower interaction energies and halogen bonding appears not sufficiently strong enough to extend the mesogenic core at elevated temperatures. Thus, no

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

• subtle differences in the reaction conditions opened up distinct reaction pathways [1][2][3][4][5]. Imines are versatile substrates that can be converted into various azo compounds, depending upon the reaction conditions [6][7][8][9]. In particular, the reactivities of N-benzylidenes have been

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

• known photocatalysts, such as aryl ketones (Scheme 3) [15][16][17]. Later, Steel and co-workers examined the photochemical properties of benzaldehyde (8), studying the EnT from 8 to azo compounds [18]. Upon the irradiation and excitation of benzaldehyde (8), the phosphorescence was quenched either by

Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• , M5S 3H6, Canada 10.3762/bjoc.15.296 Abstract Aminoazobenzene derivatives with four ortho substituents with respect to the N–N double bond are a relatively unexplored class of azo compounds that show promise for use as photoswitches in biology. Tetra-ortho-methoxy-substituted aminoazobenzene compounds

• . Species 5 could be switched with blue and green light under physiological conditions and be thermally relaxed with a half-life of 12 minutes. This relaxation rate was substantially lower than other blue-green-absorbing azo compounds without substituents in all four ortho-positions relative to the azo unit

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

• full agonism. The compound class disclosed here can aid in new photopharmacology studies of CXCR3 signaling. Keywords: azo compounds; chemokine receptor; efficacy photoswitching; G protein-coupled receptors; photopharmacology; Introduction Photopharmacology is an emerging discipline at the interface

• -nitrobenzaldehyde (8a) to give the corresponding tertiary amine 9a in high yield. The nitro group of 9a was subsequently reduced by SnCl2 in high yield. The resulting aniline 10a was used to obtain the azo compounds 12a–e in varying yields through a Mills reaction with the corresponding nitroso compounds 11a–e

• compound 9c which was reduced to aniline 10c and used to obtain the azo compounds 14a–d,f–i in variable yields through a Mills reaction with the corresponding nitroso compounds 11a-b,e–j. Methylation of 14a–d,f–i with MeI yielded compounds 4a–d,f–g,i as orange powders with ≥99% trans-isomer in moderate to

Azologization and repurposing of a hetero-stilbene-based kinase inhibitor: towards the design of photoswitchable sirtuin inhibitors

• Christoph W. Grathwol,
• Nathalie Wössner,
• Sören Swyter,
• Adam C. Smith,
• Enrico Tapavicza,
• Robert K. Hofstetter,
• Anja Bodtke,
• Manfred Jung and
• Andreas Link

Beilstein J. Org. Chem. 2019, 15, 2170–2183, doi:10.3762/bjoc.15.214

• ‐time photomodulation of sirtuins in vitro. Keywords: azo compounds; epigenetics; photoswitch; sirtuins; stilbenes; Introduction Sirtuins are protein deacylases that cleave off not only acetyl, but also other acyl groups from the ε-amino group of lysines in histones and many other substrate proteins

Cobalt bis(acetylacetonate)–tert-butyl hydroperoxide–triethylsilane: a general reagent combination for the Markovnikov-selective hydrofunctionalization of alkenes by hydrogen atom transfer

• Xiaoshen Ma and
• Seth B. Herzon

Beilstein J. Org. Chem. 2018, 14, 2259–2265, doi:10.3762/bjoc.14.201

• other nitrogen-containing SOMOphiles in the HAT reaction. Employing 4-methoxyphenyldiazonium tetrafluoroborate (5a) in our HAT conditions, the alkyl aryl azo product 7a was obtained in 92% yield (Table 1, entry 10). Due to the importance of azo compounds in synthetic organic chemistry, industrial dyes

• -methoxybenzoate (3c, not shown) afforded the azo compounds 7a and 7c in 92% and 91% yields, respectively. By comparison the yield of the azo product using allyl p-methoxybenzoate (3b, now shown) as substrate was somewhat lower (77%). Diazonium salts bearing substituents with different steric and electronic

Diastereoselective anodic hetero- and homo-coupling of menthol-, 8-methylmenthol- and 8-phenylmenthol-2-alkylmalonates

• Matthias C. Letzel,
• Hans J. Schäfer and
• Roland Fröhlich

Beilstein J. Org. Chem. 2017, 13, 33–42, doi:10.3762/bjoc.13.5

• intermolecular diastereoselective radical coupling reactions [10][11][12][13][14][15][16]. There are some examples of high diastereoselectivity in the coupling of radicals generated from azo compounds [10][11], in intramolecular coupling of radicals, that are obtained by photochemical activation [12][13][14

The in situ generation and reactive quench of diazonium compounds in the synthesis of azo compounds in microreactors

• Faith M. Akwi and
• Paul Watts

Beilstein J. Org. Chem. 2016, 12, 1987–2004, doi:10.3762/bjoc.12.186

• Faith M. Akwi Paul Watts Nelson Mandela Metropolitan University, University Way, Port Elizabeth, 6031, South Africa 10.3762/bjoc.12.186 Abstract In this paper, a micro-fluidic optimized process for the continuous flow synthesis of azo compounds is presented. The continuous flow synthesis of Sudan

• % was achieved in approximately 2.4 minutes and a small library of azo compounds was thus generated under these reaction conditions from couplers with aminated or hydroxylated aromatic systems. The scaled up synthesis of these compounds in PTFE tubing (i.d. 1.5 mm) was also investigated, where good

• methods of production. The production of azo compounds is one controversial sector of the fine chemical industry; color is highly desired and used in almost everything, but the waste generated from the production of these compounds is detrimental to the environment and human health. Following the

Synthesis of 2,1-benzisoxazole-3(1H)-ones by base-mediated photochemical N–O bond-forming cyclization of 2-azidobenzoic acids

• Daria Yu. Dzhons and
• Andrei V. Budruev

Beilstein J. Org. Chem. 2016, 12, 874–881, doi:10.3762/bjoc.12.86

• another report [39], the major products formed from triplet nitrenes are primary amines 4 through hydrogen-atom abstraction [58], secondary amines, 1,2-arylhydrazides and azo compounds 5, which are obtained by recombination of radicals [59]. Moreover, it was shown that yields of primary amines increased

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• surface from the Sun is in fact in the IR, visible and UVA regions, at wavelengths matching the energy of only a few particularly weak bonds. The result is that unappealing initiators such as peroxides or azo compounds normally have to be employed. Two different classes of materials, collectively known as

A facile synthesis of functionalized 7,8-diaza[5]helicenes through an oxidative ring-closure of 1,1’-binaphthalene-2,2’-diamines (BINAMs)

• Youhei Takeda,
• Masato Okazaki,
• Yoshiaki Maruoka and
• Satoshi Minakata

Beilstein J. Org. Chem. 2015, 11, 9–15, doi:10.3762/bjoc.11.2

• iodine-containing reagent t-BuOI, which is readily generated in situ from t-BuOCl and NaI, serves as a powerful oxidant for homo- and cross-dimerization of aromatic amines leading to aromatic azo compounds [27][28][30]. However, the employment of t-BuOI as an oxidant for this intramolecular oxidative N=N

Boron-substituted 1,3-dienes and heterodienes as key elements in multicomponent processes

• Ludovic Eberlin,
• Fabien Tripoteau,
• François Carreaux,
• Andrew Whiting and
• Bertrand Carboni

Beilstein J. Org. Chem. 2014, 10, 237–250, doi:10.3762/bjoc.10.19

• presence of Yb(fod)3 to afford 2-alkoxy-3,4-dihydro-5-vinyl-2H-pyran 33. In the presence of electron-poor dienophiles, as N-phenylmaleimide, maleic anhydride, activated azo compounds or naphthoquinone, 33 underwent normal Diels–Alder reactions thus giving the corresponding cycloadducts 34 as single

Cyclization of substitued 2-(2-fluorophenylazo)azines to azino[1,2-c]benzo[d][1,2,4]triazinium derivatives

• Aleksandra Jankowiak,
• Emilia Obijalska and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2013, 9, 1873–1880, doi:10.3762/bjoc.9.219

• , 141.2, 142.0, 145.7, 148.2, 159.2; anal. calcd for C20H19N3O4S: C, 60.44; H, 4.82; N, 10.57; found: C, 60.15; H, 4.78; N, 10.47. Azo compounds 4. A general procedure Method A. To the solution of amine (1.0 mmol) in dry CH2Cl2 (2 mL), 2-nitroso-4-picoline (7, 1.0 mmol) was added followed by a catalytic

• pattern that could be ascribed to the cation 1f was detected. Similarly unsuccessful were the attempts to cyclize azopyrazine 5 (halogen lamp/ice bath or sunlight, Figure 4) and azopyrimidine 6 (halogen lamp/reflux); instead complex mixtures of products were obtained. Synthesis of azo precursors Azo

• compounds 4b–4e were prepared in 38%–90% yield using method A (Scheme 2) in which 2-nitroso-4-picoline (7) [8] was condensed with 2-fluoroaniline (8a) or its derivatives 8c–8e. The 2-fluoro-5-hydroxymethylaniline (8e) was obtained according to a literature procedure [9]. 4-Cyano derivative 4f was prepared

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• processes, especially in the field of the selective oxygenation of hydrocarbons. Review Radical initiation by thermal decomposition Thermal decomposition of peroxides and azo-compounds is a well-known technique generally used to generate radicals in solution. Ishii and co-workers widely investigated the key

• several commercially available azo-compounds (including AIBN and 2,2’-azobis(2,4-dimethylvaleronitrile) (AMVN)) as radical initiators at different temperatures for the NHPI-catalyzed oxidation of cyclohexylbenzene (CHB) to the corresponding hydroperoxides, finding a high selectivity in the oxygenation at

• the 1-position (CHBHP, Scheme 4) [18]. The selectivity decreased rapidly with increasing conversion and temperature. The use of CHBHP itself as radical initiator in place of azo-compounds required higher temperatures (100–120 °C), leading to conversions up to 20%, but to the detriment of the

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

• Rick C. White,
• Benny E. Arney Jr. and
• Heiko Ihmels

Beilstein J. Org. Chem. 2012, 8, 1208–1212, doi:10.3762/bjoc.8.134

• loss of nitrogen from cyclic azo compounds is stepwise or concerted [6]. The photoextrusion of molecular nitrogen was employed also synthetically in the photoreaction of a benzothiadiazole to give an antiaromatic derivative of benzothiirene [7]. In another case, Griffin proposed carbene intermediates

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• undergo phototropism with a given direction. The enantiomerically pure 2- and 3-sulfinyl azo compounds are obtained with excellent regioselectivities by using a new and simple method for the synthesis of aromatic azobenzenes based on the treatment of quinone bisacetals 17 and 19 with different

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

• Raphael Reuter and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2012, 8, 877–883, doi:10.3762/bjoc.8.99

• the analysis of the photochemical properties. In this context we designed a novel strategy to access meta-oligoazobiphenyls via site-selective Mills reaction and Suzuki cross-coupling in a highly efficient iterative way. Photochemical examination of the resulting monomeric and oligomeric azo compounds

Azobenzene dye-coupled quadruply hydrogen-bonding modules as colorimetric indicators for supramolecular interactions

• Yagang Zhang and
• Steven C. Zimmerman

Beilstein J. Org. Chem. 2012, 8, 486–495, doi:10.3762/bjoc.8.55

• , the ability to synthesize these recognition units containing azobenzene units opens up the possibility to turn hydrogen bonding on and off. With regard to synthesis, aromatic azo compounds are commonly prepared by an electrophilic substitution reaction, the best partners being an electron-rich