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

• literature substrates for catalysis studies. This work is based on Andrew D. Gillie’s doctoral thesis (“Synthesis and Applications of 4N-Substituted Oxazoles”, University of Birmingham, 2015). Funding We thank EPSRC and the School of Chemistry at the University of Birmingham for studentship support (ADG, MGW

Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• functionalities, applicability to a wide range of heteroarenes and allyl halides, and high stereoselectivity (Scheme 71). The enantioselective C(sp2)–H allylation of (benz)oxazoles and benzothiazoles with γ,γ-disubstituted primary allyl phosphates catalyzed by NHC–Cu(I) complexes was reported by Ohmiya, Sawamura

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• esters. Co-catalyzed construction of C(sp2)–C(sp3) bonds. Co-catalyzed CDC of imidazo[1,2-a]pyridines with isochroman. Co-catalyzed C–H alkylation of (benz)oxazoles with ethers. Cobalt-catalyzed CDC between unactivated C(sp2)–H and C(sp3)–H bonds. MnO2-catalyzed CDC of the inactive C(sp3)-H. Oxidative

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

• of azine(pyridine)-N-oxides 9 with oxazoles 166 was reported by Miura and group [102]. Although their work majorly covered quinoline N-oxide substrates, they also investigated three pyridine substrates in the reaction leading to the corresponding products in moderate yields (Scheme 32). The N-oxide

Inline purification in continuous flow synthesis – opportunities and challenges

• Jorge García-Lacuna and
• Marcus Baumann

Beilstein J. Org. Chem. 2022, 18, 1720–1740, doi:10.3762/bjoc.18.182

• stoichiometric transformations. Many interesting examples have been reported by the Ley group [73][74]. Highlights include the early report of synthesizing of 4,5-disubstituted oxazoles, which includes a protocol to recycle columns. In this case, a packed cartridge containing a base is used: PS-BEMP (tert

One-pot synthesis of 2-arylated and 2-alkylated benzoxazoles and benzimidazoles based on triphenylbismuth dichloride-promoted desulfurization of thioamides

• Arisu Koyanagi,
• Yuki Murata,
• Shiori Hayakawa,
• Mio Matsumura and
• Shuji Yasuike

Beilstein J. Org. Chem. 2022, 18, 1479–1487, doi:10.3762/bjoc.18.155

• , and achieved the syntheses of 2-aryl- and 2-alkylbenzazoles, such as oxazoles, imidazoles, and thiazole, in satisfactory yields. The protocol was successfully applied to the synthesis of tafamidis, a clinically used drug for transthyretin amyloid inhibition. The reaction is simple, can be performed in

New efficient synthesis of polysubstituted 3,4-dihydroquinazolines and 4H-3,1-benzothiazines through a Passerini/Staudinger/aza-Wittig/addition/nucleophilic substitution sequence

• Long Zhao,
• Mao-Lin Yang,
• Min Liu and
• Ming-Wu Ding

Beilstein J. Org. Chem. 2022, 18, 286–292, doi:10.3762/bjoc.18.32

• reaction has also been utilized widely in preparation of various heterocycles under mild neutral conditions [30][31][32]. Recently we have reported the synthesis of 3H-2-benzoxepin-1-ones, 4H-3,1-benzoxazines and oxazoles by combination of a Passerini with an intramolecular aza-Wittig reaction [33][34][35

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• analysis, 1H, 13C, and 15N NMR spectroscopy, HRMS, and single-crystal X-ray diffraction data. Keywords: β-enamino ketoesters; heterocyclic amino acids; 15N-labeled 1,2-oxazole; NMR (1H; 13C; 15N); 1,2-oxazole (isoxazole); X-ray structure analysis; Introduction 1,2-Oxazoles (isoxazoles) constitute an

• -oxazoles are: the 1,3-dipolar cycloaddition of alkenes and alkynes with nitrile oxides, and the reaction of a three-carbon atom component, such as a α,β-unsaturated ketone or a 1,3-diketone with hydroxylamine hydrochloride [33]. Recently, Rosa et al. reported a useful procedure for the synthesis of various

• -oxazoles [34][35]. This study aimed to develop and synthesize methyl 5-(cycloaminyl)-1,2-oxazole-4-carboxylates, as new amino acid-like building blocks. This type of functionalized heterocycles could exhibit not only useful biological properties, but also find application as building blocks for the

1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis

• Ruan Carlos B. Ribeiro,
• Patricia G. Ferreira,
• Amanda de A. Borges,
• Luana da S. M. Forezi,
• Fernando de Carvalho da Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5

• naphtho[1,2-d]oxazoles from β-NQS. A) Arylation and vinylation of β-NQS catalyzed by Ni(II) salts. B) Transformation of the 1,2-dicarbonyl group in the fused imidazo[4,5-a] heterocycle. Benzo[a]carbazole and benzo[c]carbazoles fused with 1,2-naphthoquinone. Synthesis of 1,2-naphthoquinones having a C=C

Application of the Meerwein reaction of 1,4-benzoquinone to a metal-free synthesis of benzofuropyridine analogues

• Rashmi Singh,
• Tomas Horsten,
• Rashmi Prakash,
• Swapan Dey and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 977–982, doi:10.3762/bjoc.17.79

• novel and may have a potential medicinal interest. Conclusion In conclusion, we have successfully synthesized hydroxy-substituted pyridobenzofuran 13. Furthermore, nitration of 13 yielded two regioisomers, 14 and 15, which were further converted to oxazoles 19 and 20. Formylation of 13 was

Synthesis of N-perfluoroalkyl-3,4-disubstituted pyrroles by rhodium-catalyzed transannulation of N-fluoroalkyl-1,2,3-triazoles with terminal alkynes

• Olga Bakhanovich,
• Viktor Khutorianskyi,
• Vladimir Motornov and
• Petr Beier

Beilstein J. Org. Chem. 2021, 17, 504–510, doi:10.3762/bjoc.17.44

• -sulfonyl-1,2,3-triazoles (Scheme 1) [11][12][13][14][15][16][17]. We have recently reported that N-perfluoroalkyl-1,2,3-triazoles [18] undergo rhodium-catalyzed transannulation reactions leading to various nitrogen heterocycles, such as imidazoles, pyrrolones, imidazolones, oxazoles, azepines [19][20][21

A sustainable strategy for the straightforward preparation of 2H-azirines and highly functionalized NH-aziridines from vinyl azides using a single solvent flow-batch approach

• Michael Andresini,
• Leonardo Degannaro and
• Renzo Luisi

Beilstein J. Org. Chem. 2021, 17, 203–209, doi:10.3762/bjoc.17.20

• of vinyl azides, or by other strategies involving oximes, imines and oxazoles [24]. One appealing strategy for the preparation of 2H-azirines involves the use of readily available vinyl azides [25][26][27][28][29][30]. However, the batch cyclization of vinyl azides into the corresponding 2H-azirines

• functionalized oxazoles using acetone as the solvent (Scheme 1c) [28]. Inspired by these recent reports, we became interested in the development of an eco-friendly strategy for the safe preparation of highly functionalized NH-aziridines from acyclic precursors. Herein, we report a sustainable mixed flow-batch

Access to highly substituted oxazoles by the reaction of α-azidochalcone with potassium thiocyanate

• Mysore Bhyrappa Harisha,
• Pandi Dhanalakshmi,
• Rajendran Suresh,
• Raju Ranjith Kumar and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2020, 16, 2108–2118, doi:10.3762/bjoc.16.178

• 058, India Department of Inorganic and Physical Chemistry, Indian Institute of Science (IISc), Bangalore-560 012, India 10.3762/bjoc.16.178 Abstract The reactivity of α-azidochalcones has been explored for the preparation of highly substituted oxazoles via a 2H-azirine intermediate. The

• azidochalcones, when treated with potassium thiocyanate in the presence of potassium persulfate, lead to 2,4,5-trisubstituted oxazoles in good yields. Incidentally, 2-aminothiazoles are the products when ferric nitrate is employed instead of persulfate in the above reaction. Keywords: aminothiazole; oxazole

• -azidochalcones as the precursor [9], we herein report the preparation of highly substituted oxazoles and thiazoles. Oxazoles are ubiquitously found in various natural products [10][11][12][13][14], pharmaceuticals [15][16][17][18], functional materials [19][20] as well as in several organic building blocks [21

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• allowed a significant improvement of the reaction efficiency. The C–H coupling was compatible with a large panel of heteroaromatic substrates including benzoxazoles, oxazoles, thiazoles, and oxadiazoles, as well as non-aromatic oxazolines. Although the initial protocol necessitated the use of a

The McKenna reaction – avoiding side reactions in phosphonate deprotection

• Katarzyna Justyna,
• Joanna Małolepsza,
• Damian Kusy,
• Waldemar Maniukiewicz and
• Katarzyna M. Błażewska

Beilstein J. Org. Chem. 2020, 16, 1436–1446, doi:10.3762/bjoc.16.119

• problem. Section 1: Formation of oxazoles from propargylamides One of the most intriguing side reactions was observed when compounds comprising a propargyl amide group were treated with BTMS. Besides the products of addition of HBr, we observed the formation of oxazole. In order to study this process, we

• of acetylenic ethers gave α-halovinyl ethers [38]. HBr generated in situ from BTMS and water was also used in the synthesis of α-bromoenamides from an ynamide [39]. However, to the best of our knowledge, there are no reports on the formation of oxazoles in this manner [40]. We found that the addition

• . Since the known procedures for the syntheses of oxazoles are rather harsh and usually involve higher temperature [Pd(OAc)2, toluene, AcOH, 100 °C, 24 h [41] and/or the presence of Lewis acids (FeCl3, ACN (24 h, 80 °C) or 1,2-DCE (2 h, 80 °C), DCM (24 h, 45 °C) [40]], we envisioned that the present

Copper-based fluorinated reagents for the synthesis of CF₂R-containing molecules (R ≠ F)

• Louise Ruyet and
• Tatiana Besset

Beilstein J. Org. Chem. 2020, 16, 1051–1065, doi:10.3762/bjoc.16.92

• oxazoles (17 examples, up to 87% yield) were difluoromethylated but a variety of other heteroarenes turned out to be suitable such as pyridine, imidazole, benzo[d]thiazole, benzo[b]thiophene, benzo[d]oxazole, thiazole and thiophene derivatives (Scheme 6). Copper-based CF2FG-containing reagents Besides the

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

• have been proposed [17][73][74][75][76][77][78][79][80]. For example, Fedorova et al. have shown that after the cation-induced ring opening of spirooxazine derivatives, the respective merocyanine forms undergo a slow oxidation to the corresponding oxazoles in the dark only under aerobic conditions [17

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

• amido alcohols 154. Cyclization in the presence of tosyl chloride/triethylamine yielded the analogous ferrocenyl phosphoryl oxazoles 155, which were further reduced to give the corresponding phosphine oxazole ligands 156. The ferrocenylphosphine oxazole ligand 156 is a fascinating example which contains

• 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

Thermal stability of N-heterocycle-stabilized iodanes – a systematic investigation

• Andreas Boelke,
• Yulia A. Vlasenko,
• Mekhman S. Yusubov,
• Boris J. Nachtsheim and
• Pavel S. Postnikov

Beilstein J. Org. Chem. 2019, 15, 2311–2318, doi:10.3762/bjoc.15.223

• 12 resulted in a drastic decrease of ΔHdec to 44.9 kJ/mol. In contrast, oxazoles 13 and 14 both had a comparable ΔHdec to 9, however, these NHIs are thermally more labile (Tpeak = 159.2 and 144.0 °C). Compared to 9, diphenylimidazole-substituted NHI 15 exhibited a considerably lower ΔHdec value (39.7

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

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• -labile alkoxy substituents such as a 2-(trimethylsilyl)ethoxy group are required for the conversion of β-ketoenamides into 5-acetyl-substituted oxazoles OX, again compounds with high potential for subsequent functional group transformations. For acid labile β-ketoenamides bearing bulky substituents the

• reactions are possible. Keywords: allenes; condensations; multicomponent reactions; oxazoles; pyrimidines; quinoxalines; Introduction Multicomponent reactions are known to create unique product skeletons in an atom economic, efficient and time saving fashion. In many cases, compounds bearing functional

• particular heterocyclic compounds. The synthesis of pyrimidines PM, pyrimidine N-oxides PO, oxazoles OX, 1,2-diketones DK and quinoxalines QU starting from β-ketoenamides KE is the topic of the present review. Review Scope of the LANCA three-component synthesis of β-ketoenamides The scope of the LANCA three

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• construct them less frequently. Many biologically active synthetic compounds contain highly substituted five-membered heterocycles. In particular, pyrroles and oxazoles are quite commonly encountered (Figure 9) [58][59]. Xiao and co-workers have shown that highly substituted pyrroles can be synthesised by

• aromatic ring must lie in conjugation with the iminium double bond, making the orbitals of the ring orthogonal to the orbital in which the unpaired electron resides. The Xiao group have also published a method for making oxazoles using conditions that are very similar to those described above (Scheme 16

An unusual thionyl chloride-promoted C−C bond formation to obtain 4,4'-bipyrazolones

• Gernot A. Eller,
• Gytė Vilkauskaitė,
• Algirdas Šačkus,
• Vytas Martynaitis,
• Ashenafi Damtew Mamuye,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2018, 14, 1287–1292, doi:10.3762/bjoc.14.110

• the course of the preparation of substituted 6H-pyrazolo[4,3-d][1,2]oxazoles we thus obtained the required 4-benzoyl-5-chloropyrazoles by treatment of the relevant 4-benzoyl-5-hydroxypyrazoles with POCl3 [21]. Results and Discussion Chemistry However, the attempted reaction of ester 1a (R1 = Ph, R2

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

• significant antibacterial activity against Gram-positive bacterial strains [50]. Several other distamycin analogs were synthesized by replacing one or more pyrrole rings with other heterocycles such as pyrazoles [51], benzofurans [52], thiazoles, thiophenes, imidazole and oxazoles [53] in order to establish a

Continuous multistep synthesis of 2-(azidomethyl)oxazoles

• Thaís A. Rossa,
• Nícolas S. Suveges,
• Marcus M. Sá,
• David Cantillo and
• C. Oliver Kappe

Beilstein J. Org. Chem. 2018, 14, 506–514, doi:10.3762/bjoc.14.36

• , Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil 22941-909, Research Center Pharmaceutical Engineering GmbH (RCPE), Inffeldgasse 13, 8010 Graz, Austria 10.3762/bjoc.14.36 Abstract An efficient three-step protocol was developed to produce 2-(azidomethyl)oxazoles from vinyl azides in a

• continuous-flow process. The general synthetic strategy involves a thermolysis of vinyl azides to generate azirines, which react with bromoacetyl bromide to provide 2-(bromomethyl)oxazoles. The latter compounds are versatile building blocks for nucleophilic displacement reactions as demonstrated by their

• subsequent treatment with NaN3 in aqueous medium to give azido oxazoles in good selectivity. Process integration enabled the synthesis of this useful moiety in short overall residence times (7 to 9 min) and in good overall yields. Keywords: azirines; continuous flow; heterocycles; oxazoles; process