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

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• -free and recyclable. A variety of heteroarenes, like pyrroles, oxazoles, furanes, thiophenes, indoles and pyrazines were successfully converted into the corresponding trifluoromethylated products in moderate to good yields (Scheme 27). Remarkably, a side chlorination reaction was observed during the

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• bromination of the α-carbon using CBrCl3 as the Br source. This in situ halogenation strategy has been employed for the synthesis of quinoxalines [23], oxazoles [24][25], pyrido[1,2-a]benzimidazoles [26], imidazo[1,2-a]pyridines [27][28][29][30], thiazoles [31][32] and benzothiazoles [33][34]. With weak

Iodoarene-catalyzed cyclizations of N-propargylamides and β-amidoketones: synthesis of 2-oxazolines

• Somaia Kamouka and
• Wesley J. Moran

Beilstein J. Org. Chem. 2017, 13, 1823–1827, doi:10.3762/bjoc.13.177

• ][26][27][28][29]. Saito and co-workers have reported the cyclization of propargylamides to form oxazoles rather than oxazolines under stoichiometric and, more recently, catalytic hypervalent iodine conditions [30][31]. Various other methods for the cyclization of unsaturated amides have been reported

Oxidative dehydrogenation of C–C and C–N bonds: A convenient approach to access diverse (dihydro)heteroaromatic compounds

• Santanu Hati,
• Ulrike Holzgrabe and
• Subhabrata Sen

Beilstein J. Org. Chem. 2017, 13, 1670–1692, doi:10.3762/bjoc.13.162

• an important class of compounds [1]. A large variety of such compounds are discovered so far and their therapeutic potential in diverse disease models has been thoroughly investigated [2]. For example thiazoles and oxazoles are found in various bioactive natural products, organic dyes and

• temperature. DDQ also induced oxidative dehydrogenation in 2-thiazolidines 27 and 2-oxazolidines 28 at room temperature in the presence of 4 Å molecular sieves with dichloromethane as solvent to generate diversely substituted 2-thiazoles 29 and 2-oxazoles 30 (Scheme 7) [41]. The putative mechanism initiated

Development of a method for the synthesis of 2,4,5-trisubstituted oxazoles composed of carboxylic acid, amino acid, and boronic acid

• Kohei Yamada,
• Naoto Kamimura and
• Munetaka Kunishima

Beilstein J. Org. Chem. 2017, 13, 1478–1485, doi:10.3762/bjoc.13.146

• Kohei Yamada Naoto Kamimura Munetaka Kunishima Faculty of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan 10.3762/bjoc.13.146 Abstract A novel method for the synthesis of trisubstituted oxazoles via a

• one-pot oxazole synthesis/Suzuki–Miyaura coupling sequence has been developed. One-pot formation of 5-(triazinyloxy)oxazoles using carboxylic acids, amino acids and a dehydrative condensing reagent, DMT-MM, followed by Ni-catalyzed Suzuki–Miyaura coupling with boronic acids provided the corresponding

• 2,4,5-trisubstituted oxazoles in good yields. Keywords: one-pot oxazole synthesis; Suzuki–Miyaura coupling; triazine; 5-(triazinyloxy)oxazole; trisubstituted oxazole; Introduction Oxazoles are found in numerous natural products and are used as a broad range of artificial compounds [1][2]. In

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

Cyclisation mechanisms in the biosynthesis of ribosomally synthesised and post-translationally modified peptides

• Andrew W. Truman

Beilstein J. Org. Chem. 2016, 12, 1250–1268, doi:10.3762/bjoc.12.120

• pathways but is found across proteins of all sizes so will not be discussed here. Review Thiazole and oxazoles Thiazoles and oxazoles are found in a huge number of bacterial RiPPs, which are often loosely defined as thiazole/oxazole-modified microcins [24] (TOMMs), although these can be subdivided more

• peptides for each of these molecules. The sequence highlighted in blue in PatE corresponds to the core peptide for patellamide C, another macrocyclic RiPP that contains thiazoles and oxazolines. Formation of thiazoles and oxazoles in RiPPs. A) Biosynthesis of microcin B17. B) Mechanistic models for the

Synthesis of highly functionalized 2,2'-bipyridines by cyclocondensation of β-ketoenamides – scope and limitations

• Paul Hommes and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2016, 12, 1170–1177, doi:10.3762/bjoc.12.112

• formed. Instead, we isolated the trisubstituted oxazole derivative 6 in 55% yield. The scope of this reaction has not been studied by us, however it is known in the literature that enamides can undergo related oxidative cyclizations to oxazoles in the presence of the reagent cocktail employed or under

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

• -position of the benzisoxazole dramatically reduces the thermal stability of these compounds. Indeed, these compounds are the most labile representatives of several isomeric oxazoles [32], and they begin to decompose at temperatures slightly above 30 °C, which limits the number of methods for their

Natural products from microbes associated with insects

• Christine Beemelmanns,
• Huijuan Guo,
• Maja Rischer and
• Michael Poulsen

Beilstein J. Org. Chem. 2016, 12, 314–327, doi:10.3762/bjoc.12.34

• of mitochondrial and bacterial NADH–ubiquinone oxidoreductase (complex I) [46]. Streptochlorin (2), on the other side, belongs to the natural compound class of 5-(3-indolyl)oxazoles, and has been isolated from many different (marine) Actinobacteria species. Streptochlorin and closely related

Investigation on the reactivity of α-azidochalcones with carboxylic acids: Formation of α-amido-1,3-diketones and highly substituted 2-(trifluoromethyl)oxazoles

• Kandasamy Rajaguru,
• Arumugam Mariappan,
• Rajendran Suresh,
• Periasamy Manivannan and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2015, 11, 2021–2028, doi:10.3762/bjoc.11.219

• temperature, it affords highly substituted 2-(trifluoromethyl)oxazoles. These flexible transformations proceed under solvent free conditions in good to excellent yields without any catalyst. Keywords: α-amido-1,3-diketones; α-azidochalcones; carboxylic acids; 2H-azirines; oxazoles; Introduction α

• . The N-(2-keto)amide skeleton is of particular interest, as it serves as a synthetic precursor for various small heterocyclic compounds such as imidazoles, oxazoles and thiazoles [7][8][9]. Azirine, the smallest nitrogen-containing unsaturated three-membered heterocyclic system, is well known as a

• acid and not with other carboxylic acids. A plausible mechanism has been illustrated for the formation of substituted oxazoles (Scheme 6). Initial attack of trifluoroacetic acid on the azide via Michael addition affords active intermediate 9. Subsequently, an intramolecular nucleophilic addition takes

Cross metathesis of unsaturated epoxides for the synthesis of polyfunctional building blocks

• Meriem K. Abderrezak,
• Kristýna Šichová,
• Nancy Dominguez-Boblett,
• Antoine Dupé,
• Zahia Kabouche,
• Christian Bruneau and
• Cédric Fischmeister

Beilstein J. Org. Chem. 2015, 11, 1876–1880, doi:10.3762/bjoc.11.201

• scarcely used in olefin cross metathesis transformations. In some examples, Grela used 1 as a test substrate to evaluate the efficiency of new catalysts [26], and Cossy prepared vinyl functionalized oxazoles [27]. To our knowledge, the cross metathesis of 1 with electron-deficient olefins has not been

Azirinium ylides from α-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

• Nikolai V. Rostovskii,
• Mikhail S. Novikov,
• Alexander F. Khlebnikov,
• Galina L. Starova and
• Margarita S. Avdontseva

Beilstein J. Org. Chem. 2015, 11, 302–312, doi:10.3762/bjoc.11.35

• reversibly undergo a 1,5-cyclization to dihydroazireno[2,1-b]oxazoles. Dihydroazireno[2,1-b]oxazoles derived from 3-aryl-2H-azirines and 3-diazoacetylacetone or ethyl diazoacetoacetate are able to cycloadd to acetyl(methyl)ketene generated from 3-diazoacetylacetone under Rh(II) catalysis to give 4,6-dioxa-1

• into dihydroazireno[2,1-b]oxazoles capable of cycloadding to acyl ketenes, was discovered in the study on the reactivity of 3-monosubstituted azirines toward 3-diazoacetylacetone (2c) under catalytic conditions. The competition between ring opening and 1,5-cyclization in azirinium ylides, as well as

• –C2 bond to 2-azabuta-1,3-diene followed by 1,6-cyclization. Along with ring opening, transient azirinium ylides more readily undergo reversible 1,5-cyclization to dihydroazireno[2,1-b]oxazoles which can be trapped with such active electrophiles as acylketenes to give 4,6-dioxa-1-azabicyclo[3.2.1]oct

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

• Ivana Šagud,
• Simona Božić,
• Željko Marinić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230

• .10.230 Abstract Novel cis/trans-4- and cis/trans-5-(2-vinylstyryl)oxazoles have been synthesized by Wittig reactions from the diphosphonium salt of α,α’-o-xylene dibromide, formaldehyde and 4- and 5-oxazolecarbaldehydes, respectively. In contrast, trans-5-(2-vinylstyryl)oxazole has been synthesized by

• the van Leusen reaction from trans-3-(2-vinylphenyl)acrylaldehyde which is prepared from o-vinylbenzaldehyde and (formylmethylene)triphenylphosphorane. The 4- and 5-(2-vinylstyryl)oxazoles afford, by photochemical intramolecular cycloaddition, diverse fused oxazoline-benzobicyclo[3.2.1]octadienes

• ][23][24][25]. There are examples of oxazole photochemical intermolecular cycloadditions [26][27][28][29][30][31][32], but to the best of our knowledge, there are no examples of intramolecular photocycloaddition. We describe herein, the synthesis of new 4- and 5-(2-vinylstyryl)oxazoles (1, 2) and their

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• , oxazoles, thiazoles and triazoles incorporated into peptide structures will be described. Pyrrolidines 2-substituted pyrrolidine-based dipeptide mimics were obtained from an Ugi-4CR followed by a Pd-catalyzed Sn2 cyclization as described by Banfi et al. [51] . Herein, the Ugi reaction provided a small

• afforded the final (R)-bacillamide C in 6% yield over three steps (ee 94%). Oxazoles The oxazole unit has been applied in different bioactive marine natural products [110]. The group of Zhu reported a Ugi 3-CR to a small library of 2,4,5-trisubstituted oxazole-containing peptide-like structures from

• bifunctional α-isocyanoacetamides (Scheme 43) [111][112]. A plausible mechanism for this reaction involves the formation of 141, that after tautomerization, cyclizes to the oxazole product 143. It is noteworthy, that this reaction proceeds without the addition of a carboxylic acid because amino-oxazoles are

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• -diphenylphosphino-2-aminocyclohexane–Au(I) complex 20 (Figure 2), AgNTf2 as an additive, toluene as a solvent, rt, and a concentration of imine above 0.2 M. The obtained ee ranged from 41 to 95%. In a similar approach, Strand and co-workers [44] worked out a new entry to oxazoles 21 starting from terminal alkynes

• of Ag(I) leads to oxazoles 68 when isocyano amides or isocyano esters 66 were used as substrates. The reaction proceeds through the formation of iminium ion 67 [92]. The isocyanide carbon atom is sufficiently nucleophilic to attack iminium ion 67. Subsequent deprotonation and cyclization yields

• oxazoles 68 (Scheme 34). Another cluster of silver-mediated Mannich-type reactions involves the enantioselective addition of siloxyfurans 70 to imines 69 (vinylogous Mannich reaction, VM) affording chiral butenolide derivatives 71 (Scheme 35). The reaction proceeds in the presence of amino acid-based

Recent advances in transition metal-catalyzed Csp²-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

• Grégory Landelle,
• Armen Panossian,
• Sergiy Pazenok,
• Jean-Pierre Vors and
• Frédéric R. Leroux

Beilstein J. Org. Chem. 2013, 9, 2476–2536, doi:10.3762/bjoc.9.287

• base and an oxidant. The reaction conditions had to be slightly customized for each class of substrates. The methodology was first developed for 2-substituted 1,3,4-oxadiazoles (Cu(OAc)2/1,10-phenanthroline/t-BuONa/NaOAc/air, Table 20), then extended to benzo[d]oxazoles, benzo[d]imidazoles, benzo[d

• [114] as well as of various arenes and heteroarenes (pyridines, pyrimidines, pyrazines, quinolines, pyrroles, thiophenes, furans, pyrazoles, imidazoles, thiazoles, oxazoles, thiadiazoles, triazoles) [115]. The yields were low to excellent, depending on the substrate (Scheme 12 and Figure 20). Iron(II

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

• methods utilising cycloadditions of electron-rich oxazoles and acrylates [17][18] tri- and tetrazines with alkenes/alkynes [19] or pyrones with nitriles [20] have been used successfully to access specifically functionalised pyridines which are difficult to prepare by the more direct condensation routes. A

Gallium-containing polymer brush film as efficient supported Lewis acid catalyst in a glass microreactor

• Rajesh Munirathinam,
• Roberto Ricciardi,
• Richard J. M. Egberink,
• Jurriaan Huskens,
• Michael Holtkamp,
• Herbert Wormeester,
• Uwe Karst and
• Willem Verboom

Beilstein J. Org. Chem. 2013, 9, 1698–1704, doi:10.3762/bjoc.9.194

• model substrate, and for the formation of oxazoles by ring closure of ortho-hydroxy oximes. The catalytic activity of the microreactor could be maintained by periodic reactivation by treatment with GaCl3. Keywords: dehydration of oximes; flow chemistry; gallium; microreactors; Lewis acid catalysis

• -hydroxy group and the oxime to give ring closure to the corresponding oxazoles 11 and 12, respectively, in very good conversions. The dehydration of 1 (25 µM in acetonitrile), under similar conditions as mentioned above, was used to test the stability of the catalytic layer in the microreactor. When the

• nitriles and the ring closure of ortho-hydroxy oximes to the corresponding oxazoles. In general, our catalytic system showed faster conversions for most substrates than using lab scale conditions. XPS data, obtained on a flat silicon oxide surface, showed that on average one gallium per 2–3 styrene

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

• Cristina Tubaro,
• Marco Baron,
• Andrea Biffis and
• Marino Basato

Beilstein J. Org. Chem. 2013, 9, 246–253, doi:10.3762/bjoc.9.29

• ][40][41][42][43][44][45][46]; however, only one additional example, beyond the two early reports by Reetz and Sommer [18] and by Shi and He [19], of gold-catalysed intermolecular hydroarylation has been described, albeit concerning 2-substituted oxazoles as the reaction partner [47]. Investigations on

Identification and isolation of insecticidal oxazoles from Pseudomonas spp.

• Florian Grundmann,
• Veronika Dill,
• Andrea Dowling,
• Aunchalee Thanwisai,
• Edna Bode,
• Narisara Chantratita,
• Richard ffrench-Constant and
• Helge B. Bode

Beilstein J. Org. Chem. 2012, 8, 749–752, doi:10.3762/bjoc.8.85

• , Penryn, Cornwall, TR10 9EZ, UK Faculty of Tropical Medicine, Mahidol University, 420/6 Ratchawithi Road, Ratchathewi, Bangkok 10400, Thailand 10.3762/bjoc.8.85 Abstract Two new and five known oxazoles were identified from two different Pseudomonas strains in addition to the known pyrones pseudopyronine

• A and B. Labeling experiments confirmed their structures and gave initial evidence for a novel biosynthesis pathway of these natural oxazoles. In order to confirm their structure, they were synthesized, which also allowed tests of their bioactivity. Additionally, the bioactivities of the synthesis

• additional oxazole derivative, but which was only produced in minute amounts. WS-30581 A (6) was identified by comparing the retention time and the MS fragmentation (Supporting Information File 1, Figure S2) of the product contained in the extract, with a synthesized compound. All oxazoles showed a

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

• Jiří Kulhánek and
• Filip Bureš

Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4

• -A)2 and A-π-IM-(π-D)2 push–pull systems. An initial effort to synthesize and apply azole derivatives as CT chromophores and to study their optical (non)linearities can be ascribed to Moylan, Miller, and co-workers as early as 1993 [31][32]. Donor–acceptor-substituted imidazoles, oxazoles, and