Dioxane dibromide mediated bromination of substituted coumarins under solvent-free conditions

• Subrata Kumar Chaudhuri,
• Sanchita Roy and
• Sanjay Bhar

Beilstein J. Org. Chem. 2012, 8, 323–329, doi:10.3762/bjoc.8.35

• at C4 having no partner to couple with. Thus the incorporation of bromine at C3 (Table 1, entries 2 and 4) was established. When 1b reacted with more than two equivalents of DD, the second bromine atom was incorporated in the carbocyclic ring at C8 through aromatic electrophilic substitution (Table 1

• result (Table 1, entries 10 and 11). It is important to note that the presence of an electron-donating group (–NH2) at C6, without an alkyl substituent at C4, lead to bromination of the carbocyclic ring bearing the amino group through aromatic electrophilic substitution instead of vinylic bromination

• efficiently as that at C7 through mesomeric delocalization. Rather, it was more capable of stabilizing the positive charge in the Wheland intermediate obtained after the electrophilic attack at C5, as shown in Figure 2. Thus, bromination at C5 and C7 occurred through aromatic electrophilic substitution of the

Computational evidence for intramolecular hydrogen bonding and nonbonding X···O interactions in 2'-haloflavonols

• Tânia A. O. Fonseca,
• Matheus P. Freitas,
• Rodrigo A. Cormanich,
• Teodorico C. Ramalho,
• Cláudio F. Tormena and
• Roberto Rittner

Beilstein J. Org. Chem. 2012, 8, 112–117, doi:10.3762/bjoc.8.12

• electron acceptor (QTAIM atomic charge of −0.620 for F against −1.093 for the hydroxy oxygen), which is not so uncommon, as stated in classical textbooks on aromatic electrophilic substitution, since a resonant structure with a C=F+ contribution can take place [31]; this is shown by NBO calculations, which

Structural conditions required for the bridge lithiation and substitution of a basic calix[4]arene

• Conrad Fischer,
• Wilhelm Seichter and
• Edwin Weber

Beilstein J. Org. Chem. 2011, 7, 1602–1608, doi:10.3762/bjoc.7.188

• decade two main preparative routes for the methylene-bridge substitution of p-tert-butyltetramethoxycalix[4]arene have been established: A protocol described by Biali et al. yields a stabilized methylene carbocation through bromination that is ready for electrophilic substitution under SN1 conditions [3

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

• oxazole-4-carboxylate employing strong Cs2CO3, K3PO4 or DBU bases, through deuterium-incorporation experiments in dioxane and toluene solvents, which led in both cases to the production of C2 and C5 deuterated ethyl oxazole-4-carboxylate [64]. Thus, an electrophilic substitution-type mechanism is

• ) direct arylation of oxazoles with halides proposed by Bellina and Rossi [67]. Base-assisted, Pd(0)-catalyzed, C2-selective, direct arylation of benzoxazole proposed by Zhuralev [58]; (a) Proposed cross-coupling-type mechanism; (b) Ring-close direct C2-arylation. Electrophilic substitution-type mechanism

Synthesis and oxidation of some azole-containing thioethers

• Andrei S. Potapov,
• Nina P. Chernova,
• Vladimir D. Ogorodnikov,
• Tatiana V. Petrenko and
• Andrei I. Khlebnikov

Beilstein J. Org. Chem. 2011, 7, 1526–1532, doi:10.3762/bjoc.7.179

• here was 89%, and no formation of the mercapto-derivative was detected. The properties of azole-containing thioether can be varied by functionalization of the azole ring or oxidation of the sulfur atom, and therefore we have studied the reactivity of thioethers 3–5 in electrophilic substitution and

• unreactive compound 5. The reactivity of pyrazole-containing thioether 3 in aromatic electrophilic substitution was evaluated by using nitration and iodination reactions as examples. Nitration of compound 3, by 68% nitric acid in concentrated sulfuric acid, results in both substitution in the heterocyclic

Directed aromatic functionalization

• Victor Snieckus

Beilstein J. Org. Chem. 2011, 7, 1215–1218, doi:10.3762/bjoc.7.141

• Victor Snieckus Department of Chemistry, Queen's University, Kingston, Ontario, K7L 3N6, Canada 10.3762/bjoc.7.141 The title of this Thematic Series brings to the minds of most organic chemists the beautifully logical aromatic electrophilic substitution (SEAr) [1][2][3][4][5] and, to a lesser

Asymmetric synthesis of tertiary thiols and thioethers

• Jonathan Clayden and
• Paul MacLellan

Beilstein J. Org. Chem. 2011, 7, 582–595, doi:10.3762/bjoc.7.68

• enantioselectivity in the electrophilic substitution of 73, Hoppe made use of an extremely high kinetic H/D isotope effect observed for deprotonation in similar compounds [65]. Reaction of a test substrate demonstrated an isotope effect of kH/kD ≥ 100. A racemic mixture of 77 was lithiated in the presence of

• which they undergo electrophilic substitution [56], and 82 is remarkable in that all electrophiles, except protonating agents, react with complete inversion of configuration. Enantiopure cyclohexenyl thiocarbamates also form configurationally stable α-thioallyllithium species [68][69][70]. Lithiation of

• thiocarbamate 85 followed by methylation results in the isolation of regioisomeric products arising from electrophilic substitution at either end of the lithioallyl system (Scheme 30). In the case of the secondary thiocarbamate, the γ-substituted product 87 is preferentially formed, whilst with an N,N

One-pot gold-catalyzed synthesis of 3-silylethynyl indoles from unprotected o-alkynylanilines

• Jonathan P. Brand,
• Clara Chevalley and
• Jérôme Waser

Beilstein J. Org. Chem. 2011, 7, 565–569, doi:10.3762/bjoc.7.65

• ][7]. When considering the importance of multi-functionalized indoles, it is therefore not surprising that the aniline cyclization–electrophilic substitution sequence has been achieved by means of several metal-catalyzed domino processes (Scheme 1) [8][9][10]. Among the different π-activating metals

Highly substituted benzannulated cyclooctanol derivatives by samarium diiodide-induced cyclizations

• Jakub Saadi,
• Irene Brüdgam and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, 1229–1245, doi:10.3762/bjoc.6.141

• ][7][8][9][10][11][12][13][14][15][16][17][18]. Successful approaches include ring-closing metathesis [4], rearrangements [5], and cycloadditions [6], transition metal-catalyzed cyclizations [7][8], nucleophilic and electrophilic substitution reactions [9] as well as ring expansion reactions [10

Aromatic and heterocyclic perfluoroalkyl sulfides. Methods of preparation

• Vladimir N. Boiko

Beilstein J. Org. Chem. 2010, 6, 880–921, doi:10.3762/bjoc.6.88

A surprising new route to 4-nitro-3-phenylisoxazole

• Henning Hopf,
• Aboul-fetouh E. Mourad and
• Peter G. Jones

Beilstein J. Org. Chem. 2010, 6, No. 68, doi:10.3762/bjoc.6.68

• precursor 5, an addition product of HNO2 to the substrate 1 by a formal hetero Alder-ene reaction. Isoxazole 6 could then undergo electrophilic substitution via 7 to afford the nitroso compound 8, which in a final step would be oxidized to 4 under the reaction conditions. Previously reported approaches to 4

A stable enol from a 6-substituted benzanthrone and its unexpected behaviour under acidic conditions

• Marc Debeaux,
• Kai Brandhorst,
• Peter G. Jones,
• Henning Hopf,
• Jörg Grunenberg,
• Wolfgang Kowalsky and
• Hans-Hermann Johannes

Beilstein J. Org. Chem. 2009, 5, No. 31, doi:10.3762/bjoc.5.31

• costs 194.29 kcal mol−1. Further protonation of 15 (−223.59 kcal mol−1) generates the cation 16, which can easily undergo an internal electrophilic substitution to form the spiro compound 11 (206.49 kcal mol−1). This results in an overall exothermicity of 17.19 kcal mol−1 for the reaction 4 → 11. In

• order to explain the formation of the bicyclo[4.3.1]decane derivative 12 the enol 4 is protonated first at C-5 which releases 212.87 kcal mol−1. The benzyl cation thus generated can undergo a similar electrophilic substitution to produce the final product 12 at an effort of 206.32 kcal mol−1, resulting

Convenient method for preparing benzyl ethers and esters using 2-benzyloxypyridine

• Susana S. Lopez and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2008, 4, No. 44, doi:10.3762/bjoc.4.44

• this methodology to the synthesis of other arylmethyl ethers are included. Keywords: alcohols; alkylation; benzyl; electrophilic substitution; esters; ethers; protecting groups; reagent; Introduction As organic and medicinal chemists tackle synthetic targets of ever increasing complexity [1], the

Trifluoromethyl ethers – synthesis and properties of an unusual substituent

• Frédéric R. Leroux,
• Baptiste Manteau,
• Jean-Pierre Vors and
• Sergiy Pazenok

Beilstein J. Org. Chem. 2008, 4, No. 13, doi:10.3762/bjoc.4.13

• electron withdrawing behavior to the alkoxy group but also acts to deactivate the aromatic ring system [53]. Electrophilic Aromatic Substitution Trifluoromethoxybenzene, for example, undergoes nitration considerably (up to 5 times) more slowly than benzene. The electrophilic substitution occurs selectively

Synthesis of (–)-Indolizidine 167B based on domino hydroformylation/cyclization reactions

• Giuditta Guazzelli,
• Raffaello Lazzaroni and
• Roberta Settambolo

Beilstein J. Org. Chem. 2008, 4, No. 2, doi:10.1186/1860-5397-4-2

• substrate are the peculiar features of this process. Indeed, under the adopted experimental conditions, aldehyde 2a, as it forms, reacts further in an in situ intramolecular electrophilic substitution on position two of the pyrrole nucleus giving dihydroindolizine 3, likely via formation of the bicyclic