Mild and efficient synthesis and base-promoted rearrangement of novel isoxazolo[4,5-b]pyridines

• Vladislav V. Nikol’skiy,
• Mikhail E. Minyaev,
• Maxim A. Bastrakov and
• Alexey M. Starosotnikov

Beilstein J. Org. Chem. 2024, 20, 1069–1075, doi:10.3762/bjoc.20.94

• general synthetic scheme (Scheme 1C), commercially available 2-chloro-3-nitropyridines 1a–c were reacted with ethyl acetoacetate in the presence of NaH to give compounds 2a–c which were not isolated and directly subjected to an in situ nitrosation affording isonitroso compounds 3a–c in good yields

• method, however, the cyclization occurred under drastic conditions (NaH, DMF, 130 °C) as it was reported in patent literature [23]. We assumed that a similar synthetic route (nitrosation/SNAr) would be applicable for the synthesis of isoxazolo[4,5-b]pyridine derivatives bearing other EWG in position 3

• with DMF-DMA afforded enamines 6 which, upon nitrosation, were converted into oximes 7a–c in moderate yields (Scheme 3). When compounds 7 were treated with K2CO3 3-hydroxypyridine-2-carbonitriles 8 were obtained as sole products (Scheme 4). Apparently, a cyclization of oximes 7 to 3-formylisoxazolo[4,5

Formal total synthesis of macarpine via a Au(I)-catalyzed 6-endo-dig cycloisomerization strategy

• Jiayue Fu,
• Bingbing Li,
• Zefang Zhou,
• Maosheng Cheng,
• Lu Yang and
• Yongxiang Liu

Beilstein J. Org. Chem. 2022, 18, 1589–1595, doi:10.3762/bjoc.18.169

• developed the total synthesis of macarpine by Hofmann elimination from protoberberine by introducing rings B and C (Scheme 2a) [11]. In 1995, Ishikawa and co-workers accomplished the total synthesis via a Reformatsky reaction and aromatic nitrosation through the building of rings B and C (Scheme 2b) [12

Synthetic strategies of phosphonodepsipeptides

• Jiaxi Xu

Beilstein J. Org. Chem. 2021, 17, 461–484, doi:10.3762/bjoc.17.41

• -diazoalkylphononates can be readily prepared from the corresponding 1-aminoalkylphosphonates via nitrosation with amyl nitrite. Conclusion Phosphonodepsipeptides are phosphorus analogues of depsipeptides. They are more stable than the corresponding phosphonopeptides and have been widely used as enzyme inhibitors

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• nitrosation (with sodium nitrite in acetic acid), and in Mannich reactions [12]. For the formation of dimers 5, various mechanisms were envisaged. Nevertheless, the formation of any dimer-like product structurally similar to 3a has not been observed so far. In this report we describe our efforts to extend the

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

• isoxazolines 123 or cyclic nitrones 124 with an additional oxime group (Scheme 40) [130]. The authors showed that the initial product of the oxidative cyclization of oxime 122a under the action of TBN was the dimer 127 of the nitroso compound 126, which was formed, presumably, as a result of nitrosation of the

Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate

• Andrew T. King,
• Hugh G. Hiscocks,
• Lidia Matesic,
• Mohan Bhadbhade,
• Roger Bishop and
• Alison T. Ung

Beilstein J. Org. Chem. 2019, 15, 1347–1354, doi:10.3762/bjoc.15.134

• . describes reliable routes to particularly fused aromatic 1H and 3H-indazoles [24]. The common synthetic routes for the formation of cyclic 1H-indazoles are diazotisation of corresponding o-alkylanilines [25] and nitrosation of the N-acetyl derivatives of 2-alkylanilines (Jacobson modification) [26][27][28

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

• nitrosation and subsequent heating [28], by heating with an aqueous NaHSO3 solution [29], and by photochemistry [30][31]. In nearly all cases these reactions have been carried out with 2-pyrazolin-5-ones unsubstituted at pyrazole C4 position or with derivatives carrying an alkyl or aryl substituent at the

Continuous flow nitration in miniaturized devices

• Amol A. Kulkarni

Beilstein J. Org. Chem. 2014, 10, 405–424, doi:10.3762/bjoc.10.38

• nitration of thioureas is based on subsequent nitrosation and nitration steps. The same group also analyzed continuous processes to perform the strongly exothermic nitration of naphthalene (47) (Scheme 14) with N2O5, both in the gas phase and in the liquid phase [49][50]. The authors reported that the

The first example of the Fischer–Hepp type rearrangement in pyrimidines

• Inga Cikotiene,
• Mantas Jonusis and
• Virginija Jakubkiene

Beilstein J. Org. Chem. 2013, 9, 1819–1825, doi:10.3762/bjoc.9.212

• -pyrimidinediamines. It was found that the outcome of the reaction strongly depends on the structure of the pyrimidines. Activation of the pyrimidine ring by three groups with a positive mesomeric effect is crucial for the intramolecular nitroso group migration. Keywords: Fischer–Hepp rearrangement; nitrosation; 5

• rebuttal to the article about the electrophilic nitrosation of selected pyrimidines [15]. We showed that instead of the previously reported electrophilic attack of the C-5 by NO+, the secondary amino substituents in position 4 of the pyrimidine ring underwent N-nitrosation reactions (Scheme 2). We also

• reaction of commercially or synthetically available 4,6-dichloropyrimidines with an excess of primary amines in boiling 2-propanol. As it is was shown by us earlier, the starting compounds 1 underwent smooth and high-yielding N-nitrosation reactions by using sodium nitrite in acetic acid at room

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

• Kristina Butković,
• Željko Marinić,
• Krešimir Molčanov,
• Biserka Kojić-Prodić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

• ), nitrosation and ring closure with acetic acid anhydride (30 and 40% yield). The products were submitted to photochemical and thermal intramolecular [3 + 2] cycloadditions to afford diverse heteropolycyclic compounds. Photochemical reactions afforded cis-3-(4-methylphenyl)-3a,8-dihydro-3H-pyrazolo[5,1-a

An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals

• Marcus Baumann,
• Ian R. Baxendale,
• Steven V. Ley and
• Nikzad Nikbin

Beilstein J. Org. Chem. 2011, 7, 442–495, doi:10.3762/bjoc.7.57

• by nitrosation of tert-butyl acetoacetate (37) [9], is reduced by zinc to give an unstable aminoketone intermediate. Subsequent enamine formation and ring closure affords the fully substituted pyrrole ring 40. Selective deprotection of the tert-butyl ester with concomitant decarboxylation yields

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32