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

• -azabicyclo[3.2.1]oct-2-ene and/or 5,7-dioxa-1-azabicyclo[4.3.1]deca-3,8-diene-2-one derivatives. According to DFT calculations (B3LYP/6-31+G(d,p)), the cycloaddition can involve two modes of nucleophilic attack of the dihydroazireno[2,1-b]oxazole intermediate on acetyl(methyl)ketene followed by aziridine

• the mechanism of trapping of dihydroazireno[2,1-b]oxazole intermediates by acetyl(methyl)ketene were investigated by the DFT method. Results and Discussion Rhodium(II) carbenoids generated from α-diazoketones or 2-diazo-1,3-diketones react with various nitrogen-containing compounds, such as amines [16

• involves the 1,5-cyclization of azirinium ylide 9f–h to dihydroazireno[2,1-b]oxazole 10f–h followed by cycloaddition of the latter to ketene 12 to give two regioisomeric adducts 6f,g and 7f–h (Scheme 3). Several examples of the 1,5-cyclization of azomethine ylides bearing an α-keto group into oxazole

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

• solvent mixture at 100–110 °C for 18 h. The oxazole moiety also acts as the directing group in the acetoxylation of alkyl groups with Pd(OAc)2/AcOOt-Bu or Pd(OAc)2/lauroyl peroxide oxidative systems; in these reactions acetic anhydride served as the source of the acetoxy groups [88]. Recently, Cu(OAc)2

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

Beilstein J. Org. Chem. 2014, 10, 2858–2873, doi:10.3762/bjoc.10.303

• solution and dichloromethane is employed as electrolyte. The method features attractive yields (70–95%) and a broad scope with regard to substitution on the phenylene moiety (R1 and R2) and on the oxazole unit (R3). 2 Intermolecular cyclizations 2.1 Cycloadditions with anodically generated intermediates A

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

• )oxazole small quantities of electrocyclization product, 4-(1,2-dihydronaphthalen-2-yl)oxazole, are isolated and spectroscopically characterized. Keywords: bicyclo[3.2.1]octane; intramolecular photocycloaddition; oxazole; styryl; vinyl; Introduction The bicyclo[3.2.1]octane skeleton is the basic

• ] and sydnones [11][12][13], as routes to polycyclic compounds, we turned our attention to oxazole derivatives. The oxazole structure is commonly found in natural products and pharmaceuticals [14][15][16][17] and is applied in useful reagents and intermediates in organic synthesis [18][19][20][21][22

Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

• Alexander F. Khlebnikov,
• Mikhail S. Novikov,
• Yelizaveta G. Gorbunova,
• Ekaterina E. Galenko,
• Kirill I. Mikhailov,
• Viktoriia V. Pakalnis and
• Margarita S. Avdontceva

Beilstein J. Org. Chem. 2014, 10, 1896–1905, doi:10.3762/bjoc.10.197

• very low activation barriers (0.2–1.5 kcal/mol) to give (3Z)-1-oxa-5-azahexa-1,3,5-trienes. This is expected, because the oxazole N–O bond is very weak and the reaction is pseudopericyclic [21][22]. The calculated low thermodynamic and kinetic stabilities of the isoxazolium ylides (Figure 1) give only

• )] computed at DFT B3LYP/6-31G(d) level. Energy profiles for the transformations of (3Z)-1-oxa-5-azahexa-1,3,5-triene D and oxazines E derived from (methoxycarbonyl)phenylcarbene or di(methoxycarbonyl)carbene and oxazole A. Relative free energies [kcal/mol, 298 K, CH2Cl2 (PCM)] computed at DFT B3LYP/6-31G(d

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

• 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

• unstable under acidic conditions. In total, six different aldehydes, twelve amines and three isocyanides yielded the corresponding desired oxazole mimics 143 in good yields (60–96%), however, the products were obtained as racemates even when the reaction was performed with chiral isocyanides. Some

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

• reaction with the chloride ion released during the initial imine acylation. Finally, a combination between Brønsted acid and metal catalysis, promote the isomerization of V to oxazole 21. It is noteworthy, that the gold catalyst seemed to be essential only for the formation of the gold-acetylide

Total synthesis and cytotoxicity of the marine natural product malevamide D and a photoreactive analog

• Werner Telle,
• Gerhard Kelter,
• Heinz-Herbert Fiebig,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2014, 10, 316–322, doi:10.3762/bjoc.10.29

• 13C NMR signals of oxazole C-5 (10 Hz) and C-4 (6.2 Hz). To the best of our knowledge, this is only the second time that a peptide-derived oxazol-5-ylphosphate has been characterized. Earlier, Boyd and co-workers had converted an oxazolone to an oxazolyl phosphate by treatment with excess diphenyl

New tridecapeptides of the theonellapeptolide family from the Indonesian sponge Theonella swinhoei

• Annamaria Sinisi,
• Barbara Calcinai,
• Carlo Cerrano,
• Henny A. Dien,
• Angela Zampella,
• Claudio D’Amore,
• Barbara Renga,
• Stefano Fiorucci and
• Orazio Taglialatela-Scafati

Beilstein J. Org. Chem. 2013, 9, 1643–1651, doi:10.3762/bjoc.9.188

• oxazole or thiazole rings) [10], papuamides (HIV inhibitory macrocyclic depsipeptides) [11], polytheonamides (cytotoxic linear polypeptides) [12], cyclotheonamides (thrombin and serine protease inhibitors) [13], perthamides (anti-inflammatory cyclopeptides) [14][15], solomonamides [16] and

Synthesis and physicochemical characterization of novel phenotypic probes targeting the nuclear factor-kappa B signaling pathway

• Paul M. Hershberger,
• Satyamaheshwar Peddibhotla,
• E. Hampton Sessions,
• Daniela B. Divlianska,
• Ricardo G. Correa,
• Anthony B. Pinkerton,
• John C. Reed and
• Gregory P. Roth

Beilstein J. Org. Chem. 2013, 9, 900–907, doi:10.3762/bjoc.9.103

• cell line and >400-fold selective over both the NF-κB activation in HEK 293T cells and against TNFα-mediated NF-κB activation. In comparison, the second oxazole-based probe 12 is also potent (0.2 μM) in the 697 pre-B cell line and >400-fold selective over both the NF-κB activation in HEK 293T cells and

• 4-ethoxybenzaldehyde was condensed with diacetyl monoxime under acidic conditions. The resulting oxazole N-oxide 9 was converted to the chloromethyloxazole 10 via selective chlorination with phosphorous oxychloride in good yield. Addition of thioglycolic acid led to the carboxylic acid 11, which was

Synthesis of 5-(ethylsulfonyl)-2-methoxyaniline: An important pharmacological fragment of VEGFR2 and other inhibitors

• Miroslav Murár,
• Gabriela Addová and
• Andrej Boháč

Beilstein J. Org. Chem. 2013, 9, 173–179, doi:10.3762/bjoc.9.20

• sodium salt C was subsequently converted to the hydrochloride salt of 3-amino-4-hydroxybenzene-1-sulfonyl chloride (D) by treatment with thionyl chloride at room temperature. The amino group of D was protected in the form of a 2-methylbenzo[d]oxazole-5-sulfonyl chloride (E) by reaction of D with (EtO)3CH

Engineering of indole-based tethered biheterocyclic alkaloid meridianin into β-carboline-derived tetracyclic polyheterocycles via amino functionalization/6-endo cationic π-cyclization

• Piyush K. Agarwal,
• Meena D. Dathi,
• Mohammad Saifuddin and
• Bijoy Kundu

Beilstein J. Org. Chem. 2012, 8, 1901–1908, doi:10.3762/bjoc.8.220

• antagonistic [4] and antitopoisomerase-I activities [5][6][7][8][9][10][11][12][13][14][15][16]. The presence of a heterocyclic ring at the position 3 of the indole represents an important class of marine alkaloids, such as oxazole (martefragin [17], amazol [18]), imidazole (topsentins [19][20] and

Parallel solid-phase synthesis of diaryltriazoles

• Matthias Wrobel,
• Jeffrey Aubé and
• Burkhard König

Beilstein J. Org. Chem. 2012, 8, 1027–1036, doi:10.3762/bjoc.8.115

• , 4.25; N, 23.75. Terphenyl scaffold 1 [13][14]; oxazole-pyridazine-piperazine 2 [14][15] and aryl-triazoles 3 and 4 [15][16] as α-helix mimetics. Synthesis of azido-functionalized resins 7 and 9. Copper-catalyzed [2 + 3] cycloadditions of resin-bound azide 7 with five terminal alkynes. Copper-catalyzed

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

• intermediates were also investigated revealing interesting biological activities for several compounds despite their overall simple structures. Keywords: insecticidal activity; labradorin; oxazole; Pseudomonas; secondary metabolite; Findings During our search for novel natural products from entomopathogenic

• known oxazole derivatives labradorin 1 (3, 241.1 m/z [M + H]+, C15H16N2O), labradorin 2 (4, 255.2 m/z [M + H]+, C16H18N2O) and pimprinaphine (5, 275.1 m/z [M + H]+, C18H14N2O) (Figure 1) [8][9]. Detailed analysis of the HPLC–MS data showed WS-30581 A (6, 227.1 m/z [M + H]+, C14H14N2O) [10] as an

• 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

• shifted CT bands (λmax), the lowest frequency of CN stretch (23b), and the highest calculated average second-order polarizabilities β within the studied series of compounds 21–26. The nonlinear optical properties of donor- and acceptor-substituted five-membered heterocycles, such as imidazole, oxazole

Recent advances in direct C–H arylation: Methodology, selectivity and mechanism in oxazole series

• Cécile Verrier,
• Pierrik Lassalas,
• Laure Théveau,
• Guy Quéguiner,
• François Trécourt,
• Francis Marsais and
• Christophe Hoarau

Beilstein J. Org. Chem. 2011, 7, 1584–1601, doi:10.3762/bjoc.7.187

• direct (hetero)arylation of (hetero)arenes is an attractive alternative to traditional Kumada, Stille, Negishi and Suzuki–Miyaura cross-coupling reactions, notably as it avoids the prior preparation and isolation of (hetero)arylmetals. Developments of this methodology in the oxazole series are reviewed

• in this article. Methodologies, selectivity, mechanism and future aspects are presented. Keywords: ate complex; catalytic direct arylation; mechanism; oxazole; selectivity; transition-metal catalysis; Introduction Deprotonative metalation of aromatics is widely used as a powerful method for

• the ring-close oxazole, a trend that is evidenced by 1H NMR spectroscopy and attributed to the strong covalent carbon–zinc bond along with the zinc’s low oxophilicity, and this thus allows subsequent palladium-catalyzed Negishi cross-coupling [31][32][33]. This first, highly efficient, stoichiometric

Palladium-catalyzed formation of oxazolidinones from biscarbamates: a mechanistic study

• Benan Kilbas and
• Metin Balci

Beilstein J. Org. Chem. 2011, 7, 246–253, doi:10.3762/bjoc.7.33

• -3,3a,5a,6,6a,6b-hexahydro-2H-cyclopropa[3,4]benzo[1,2-d][1,3]oxazole-6-carboxylate (9): Tris(dibenzylideneacetone)dipalladium chloroform complex (0.2 g, 193.6 mmol) was dissolved in freshly distilled THF (20 mL) under a nitrogen atmosphere. Triisopropyl phosphite (1.6 mL) in THF (5 mL) was then added

• , 11.75. Found: C, 53.21; H, 4.46; N, 7.79; S, 11.91. rel-3aR,5aR,6R,6aS,6bS-2-Oxo-3-tosyl-3,3a,5a,6,6a,6b-hexahydro-2H-cyclopropa[3,4]benzo[1,2-d][1,3]oxazole-7-exo-carbonitril (17): Biscarbamate 16 (1.00 g, 1.83 mmol) was reacted with freshly prepared Pd-complex as described above. The product was

• , 58.17; H, 4.27; N, 8.48; S, 9.71. Found: C, 58.13; H, 4.31; N, 8.41; S, 9.3. rel-3aR,5aR,6R,6aS,6bS-2-Oxo-3-tosyl-3,3a,5a,6,6a,6b-hexahydro-2H-cyclopropa[3,4]benzo[1,2-d][1,3]oxazole-7-endo-carbonitril (20): Biscarbamate 16 (1.00 g, 1.83 mmol) was reacted with freshly prepared Pd-complex as described

Low temperature enantiotropic nematic phases from V-shaped, shape-persistent molecules

• Matthias Lehmann and
• Jens Seltmann

Beilstein J. Org. Chem. 2009, 5, No. 73, doi:10.3762/bjoc.5.73

• recently suggested by a theoretical work from Vanakaras [35], in which three different uniaxial and biaxial nematic phases based on aggregates or clusters have been proposed. The model is further supported by results obtained from a bent-shaped oxazole derivative, which forms polar clusters in the nematic

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

Synthesis of 2-substituted 9-oxa-guanines {5-aminooxazolo[5,4-d]pyrimidin- 7(6H)-ones} and 9-oxa-2-thio- xanthines {5-mercaptooxazolo[5,4-d]pyrimidin- 7(6H)-ones}

• Subrata Mandal,
• Wen Tai Li,
• Yan Bai,
• Jon D. Robertus and
• Sean M. Kerwin

Beilstein J. Org. Chem. 2008, 4, No. 26, doi:10.3762/bjoc.4.26

• unsuccessful. An alternative route was sought in which the oxazole ring was formed first, followed by elaboration of the pyrimidine ring. Our previous work had demonstrated that in the case of ethyl 5-amino-2-methyloxazole-4-carboxylate 3a [20], direct annulation with chloroformamidine in DMSO at 120 °C or