Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

The synthesis of active pharmaceutical ingredients (APIs) using continuous flow chemistry

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 1194–1219, doi:10.3762/bjoc.11.134

• syntheses of two lead compounds reported earlier by AstraZeneca. The first one details the flow synthesis of a potent 5HT1B antagonist (28) that was assembled through a five step continuous synthesis including a SNAr reaction, heterogeneous hydrogenation, Michael addition–cyclisation and final amide

• temperature SNAr reactions as key flow steps in the sequence (Scheme 7). One of the early published examples of industry-based research on multi-step flow synthesis of a pharmaceutical was reported in 2011 by scientists from Eli Lilly/UK and detailed the synthesis of fluoxetine 46, the API of Prozac [60]. In

• flow reactor simplifies the practical aspects of the transformation, however, extra precautions were required in order to address and remove any leftover methylamine that would pose a significant hazard during scaling up. The final arylation of 50 was intended to be performed as a SNAr reaction

Syntheses of fluorooxindole and 2-fluoro-2-arylacetic acid derivatives from diethyl 2-fluoromalonate ester

• Antal Harsanyi,
• Graham Sandford,
• Dmitri S. Yufit and
• Judith A.K. Howard

Beilstein J. Org. Chem. 2014, 10, 1213–1219, doi:10.3762/bjoc.10.119

• the diester 3 after the initial SNAr step was not necessary and decarboxylation of crude diester 3 gave 4a very efficiently. Consequently, in all analogous experiments (Table 1), crude product diesters of type 3 were isolated and used without further purification, allowing the ready synthesis of a

• structure of 3. Molecular structure of methyl ester 6a. Molecular structure of 7. SNAr reaction of 2-fluoronitrobenzene (2a) with diethyl 2-fluoromalonate (1). Synthesis of benzyl fluoride derivative 5. Synthesis of pyridyl fluoride 7. SNAr reactions using fluoromalonate derivatives. Synthesis of methyl

Preparation of phosphines through C–P bond formation

• Iris Wauters,
• Wouter Debrouwer and
• Christian V. Stevens

Beilstein J. Org. Chem. 2014, 10, 1064–1096, doi:10.3762/bjoc.10.106

• simple phosphines [137][138][148][149]. The group of Imamoto reported the SNAr reaction of P-chiral secondary phosphine boranes 13c with halobenzenechromium complexes 72 in the presence of sec-butyllithium [150]. The stereochemistry at the phosphorus atom was retained during the substitution when it was

• electronegative fluorine atom is needed for the SNAr reaction to take place, even though the arenechromium complexes are already very electron-deficient aromatic compounds. The same group also developed a P-chiral ligand, QuinoxP 74, via deprotonation of chiral secondary phosphine borane 13d with n-butyllithium

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

• combination of deprotection and activation is also possible and is found in the literature as an Ugi Deprotection/Activation–Cyclisation (UDAC). In addition, other MCR-post-condensation reactions, especially for macrocycles, include intramolecular aryl couplings, amidations, SnAr reactions, nucleophilic

Flow microreactor synthesis in organo-fluorine chemistry

• Hideki Amii,
• Aiichiro Nagaki and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2013, 9, 2793–2802, doi:10.3762/bjoc.9.314

• tripeptide byproduct. Nucleophilic aromatic substitution (SNAr) chemistry contributes to creating useful materials. In 2005, Comer and Organ reported SNAr reactions of 2-fluoronitrobenzene using a flow microreactor system with microwave irradiation (Scheme 9) [69]. Toward making compound-libraries, Schwalbe

• explored a flow microreactor system for sequential transformation towards fluoroquinolone antibiotics such as ciprofloxacin via both inter- and intramolecular SNAr reactions (Scheme 10) [70]. Starting from the acylation reaction of (N-dimethylamino)acrylate with 2,4,5-trifluorobenzoic acid chloride

• [18F]-radiolabeled molecular imaging probes. Flow microreactor synthesis of dipeptides. Flow synthesis involving SNAr reactions. Flow synthesis of fluoroquinolone antibiotics. Highly controlled formation of PFPMgBr. Selective flow synthesis of photochromic diarylethenes. Flow microreactor system for

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

• structures of pioglitazone and rosiglitazone show common structural features bearing a distal pyridine ring linked to the thiazolidinedione pharmacophore. In rosiglitazone the pyridine unit is introduced via an SNAr reaction between N-methylethanolamine (1.44) and 2-chloropyridine (1.43) which in turn is

• readily prepared by chlorination of 2-pyridone (1.42) with phosphorous oxychloride (Scheme 8) [31][32]. The resulting primary alcohol 1.45 is then subjected to a second SNAr reaction with 4-fluorobenzaldehyde [33]. A Knoevenagel condensation of the aldehyde functionality in compound 1.47 with

• strong P1 base polymer-supported BEMP gave the corresponding ether adduct which was then converted to the desired secondary amine 1.64 via direct amidation and borane-mediated reduction. Next an SNAr reaction on 2-fluoropyridine (1.66) followed by oxidation of the benzylic alcohol using immobilised

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

• pyrimidine core toward subsequent substitution. The usage of very harsh reaction conditions (prolonged heating for hours or days, high pressure or microwave irradiation of the reaction mixtures) is required to carry out the second SNAr reaction (Scheme 1) [9][10][11][12][13][14]. In 2012 we published a

Utilizing the σ-complex stability for quantifying reactivity in nucleophilic substitution of aromatic fluorides

• Magnus Liljenberg,
• Tore Brinck,
• Tobias Rein and
• Mats Svensson

Beilstein J. Org. Chem. 2013, 9, 791–799, doi:10.3762/bjoc.9.90

• include both neutral (NH3) and anionic (MeO−) nucleophiles are quite satisfactory (r = 0.93 to r = 0.99), and SS is thus useful for quantifying both global (substrate) and local (positional) reactivity in SNAr reactions of fluorinated aromatic substrates. A mechanistic analysis shows that the geometric

• QM methods and other parts with MM methods, for example, in enzymes where the active site can be modeled with QM and the remaining structure with MM methods. Predictive models for the SNAr reaction This paper is a continuation of our work on the predictive computational modeling of the synthetically

• and industrially important SNAr and SEAr reactions (nucleophilic and electrophilic aromatic substitution, respectively) [3][4][5]. The putative mechanism for the SNAr reaction involves attack of a nucleophile and the formation of an intermediate σ-complex (also called the Meisenheimer complex

Synthesis of SF₅-containing benzisoxazoles, quinolines, and quinazolines by the Davis reaction of nitro-(pentafluorosulfanyl)benzenes

• Petr Beier and
• Tereza Pastýříková

Beilstein J. Org. Chem. 2013, 9, 411–416, doi:10.3762/bjoc.9.43

• Umemoto’s two-step procedure starting from diaryldisulfides or mercaptoaromatics [21]. We have recently reported SNAr reactions of the nitro group in compounds 3 and 4 with alkoxides and thiolates [22], vicarious nucleophilic substitution (VNS) of the hydrogen with carbon [23][24], oxygen [25] and nitrogen

From bead to flask: Synthesis of a complex β-amido-amide for probe-development studies

• Kevin S. Martin,
• Cristian Soldi,
• Kellan N. Candee,
• Hiromi I. Wettersten,
• Robert H. Weiss and
• Jared T. Shaw

Beilstein J. Org. Chem. 2013, 9, 260–264, doi:10.3762/bjoc.9.31

• available 7 was converted to methyl ester 15 in 90% yield, due to its ease of handling (Scheme 2) [20]. Next, SNAr displacement of the fluoride of 15 by N-(3-aminopropyl)pyrrolidine (8) proceeded in high yield, 99%, to give aniline 16 [20]. Reduction of the nitro group was nearly quantitative and subsequent

• (11), malonic acid and ammonium acetate under reflux proceeded smoothly, as previously described, to furnish β-amino acid 21 in 73% yield [18]. Methylation of 21 (80%) followed by nitration of 22 (67%), boc protection of 23 and SNAr displacement of the fluoride in 24 with amine 8 (71% over two steps

Asymmetric synthesis of host-directed inhibitors of myxoviruses

• Terry W. Moore,
• Kasinath Sana,
• Dan Yan,
• Pahk Thepchatri,
• John M. Ndungu,
• Manohar T. Saindane,
• Mark A. Lockwood,
• Michael G. Natchus,
• Dennis C. Liotta,
• Richard K. Plemper,
• James P. Snyder and
• Aiming Sun

Beilstein J. Org. Chem. 2013, 9, 197–203, doi:10.3762/bjoc.9.23

• was reduced under hydrogenation conditions to provide aniline 5. o-Fluoronitrobenzene (6) was coupled with the previously formed aniline under SNAr conditions to furnish anilino nitrobenzene 7a (Scheme 1). Alternatively, meta- and para-nitrophenylethanols 8 were combined with o-fluoronitrobenzene (6

Palladium-catalyzed C–N and C–O bond formation of N-substituted 4-bromo-7-azaindoles with amides, amines, amino acid esters and phenols

• Rajendra Surasani,
• Dipak Kalita,
• A. V. Dhanunjaya Rao and
• K. B. Chandrasekhar

Beilstein J. Org. Chem. 2012, 8, 2004–2018, doi:10.3762/bjoc.8.227

• 7-azaindole scaffolds appear in various pharmaceutically important molecules (Figure 1), which are very challenging and lengthy to prepare by the traditional methods [40][41]. In general, nucleophilic aromatic substitution (SNAr) reaction of a halo-precursor of 7-azaindole with a large excess of

• achieved from the corresponding halide by SNAr displacement reactions, which typically require very high temperatures, extended reaction times, and a large excess of the amine counterpart [5]. Other alternative methods employ the amino-substituted azaindole as the key intermediate, which are challenging to

Organocatalytic asymmetric Michael addition of unprotected 3-substituted oxindoles to 1,4-naphthoquinone

• Jin-Sheng Yu,
• Feng Zhou,
• Yun-Lin Liu and
• Jian Zhou

Beilstein J. Org. Chem. 2012, 8, 1360–1365, doi:10.3762/bjoc.8.157

• . Only Sammakia tried the SNAr reaction of unprotected 3-phenyloxindole with chiral electron-deficient 5-halooxazoles, promoted by 1.0 equiv of Cs2CO3 [21], with ca. 1:1 diastereoselectivity obtained. In this context, we are interested in the catalytic economical asymmetric diverse synthesis of 3,3

Exploring chemical diversity via a modular reaction pairing strategy

• Joanna K. Loh,
• Sun Young Yoon,
• Thiwanka B. Samarakoon,
• Alan Rolfe,
• Patrick Porubsky,
• Benjamin Neuenswander,
• Gerald H. Lushington and
• Paul R. Hanson

Beilstein J. Org. Chem. 2012, 8, 1293–1302, doi:10.3762/bjoc.8.147

• nucleophilic aromatic substitution (SNAr) diversification pathway is reported. Eight benzofused sultam cores were generated by means of a sulfonylation/SNAr/Mitsunobu reaction pairing protocol, and subsequently diversified by intermolecular SNAr with ten chiral, non-racemic amine/amino alcohol building blocks

• . Computational analyses were employed to explore and evaluate the chemical diversity of the library. Keywords: benzoxathiazocine 1,1-dioxides; chemical diversity; informatics; nucleophilic aromatic substitution (SNAr); sultams; Introduction The demand for functionally diverse chemical libraries has emerged, as

• , namely sulfonylation, Mitsunobu alkylation and SNAr, which when combined in different sequences or with different coupling reagents, give access to skeletally diverse sultams, including the title compounds and the 8-membered bridged, benzofused sultams [32]. Building on this strategy, we herein report

Highly selective synthesis of (E)-alkenyl-(pentafluorosulfanyl)benzenes through Horner–Wadsworth–Emmons reaction

• George Iakobson and
• Petr Beier

Beilstein J. Org. Chem. 2012, 8, 1185–1190, doi:10.3762/bjoc.8.131

• the only known SEAr of 1 or 2 is the nitration of 2 under harsh conditions and in low yield [14], we have recently described SNAr of the nitro group in compounds 1 and 2 with alkoxides and thiolates [15], vicarious nucleophilic substitution (VNS) of the hydrogen with carbon [16], oxygen [17] and

Synthesis and structure of tricarbonyl(η⁶-arene)chromium complexes of phenyl and benzyl D-glycopyranosides

• Thomas Ziegler and
• Ulrich Heber

Beilstein J. Org. Chem. 2012, 8, 1059–1070, doi:10.3762/bjoc.8.118

• the aromatic ring and, thus, making the arene more susceptible towards SNAr reactions. Likewise, the benzylic and homo-benzylic positions in tricarbonyl(η6-arene)chromium complexes are more acidic and more prone to solvolysis, nucleophilic substitution and deprotonation than in the parent arenes due

Derivatives of phenyl tribromomethyl sulfone as novel compounds with potential pesticidal activity

• Krzysztof M. Borys,
• Maciej D. Korzyński and
• Zbigniew Ochal

Beilstein J. Org. Chem. 2012, 8, 259–265, doi:10.3762/bjoc.8.27

• tribromomethyl phenyl sulfone derivatives as novel potential pesticides is reported. The title sulfone was obtained by following three different synthetic routes, starting from 4-chlorothiophenol or 4-halogenphenyl methyl sulfone. Products of its subsequent nitration were subjected to the SNAr reactions with

• . Keywords: 2-nitroaniline derivatives; phenylhydrazones; pesticides; SNAr reaction; tribromomethyl sulfone derivatives; Introduction The rapid growth of the world population results in a continous increase in the demand for food. At the same time, about 35% of the global crops around the world are being

• (compared to 94% for chlorine analogue 1), while the subsequent nitration of 6' resulted in 94% yield (compared to 96% for analogue 6). With these results at hand, we ultimately picked chlorine-containing nitrosulfone 6 as the substrate for the subsequent synthetic steps. A range of SNAr reactions of 6 with

Translation of microwave methodology to continuous flow for the efficient synthesis of diaryl ethers via a base-mediated S_NAr reaction

• Charlotte Wiles and
• Paul Watts

Beilstein J. Org. Chem. 2011, 7, 1360–1371, doi:10.3762/bjoc.7.160

• employed. To demonstrate the advantages associated with microreaction technology a series of SNAr reactions were performed under continuous flow by following previously developed microwave protocols as a starting point for the investigation. By this approach, an automated microreaction platform (Labtrix

• -temperature flow reactors, which can be scaled to increase production volume without changing the reaction conditions employed [23][24][25], resulting in a reduction in energy usage per mole. With this in mind, we report herein the translation, and further development, of a microwave method for the SNAr

• illustrating Labtrix® S1, the automated microreactor development apparatus from Chemtrix BV (NL), used for the evaluation described herein. Schematic illustrating the 10 µL reactor manifold used for the SNAr reactions described herein (3223; Chemtrix BV, NL), with the important features highlighted. Schematic

Directed aromatic functionalization

• Victor Snieckus

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

• extent, nucleophilic aromatic substitution (SNAr) [2][6][7] reactions as taught to many generations of students in their first organic chemistry courses [8] (Figure 1). Being less steeped in history, radical nucleophilic substitution (SRN1) [9] and vicarious nucleophilic substitution (VNS) [10][11][12

• heteroaromatics [15][16][17]. While comparison with SEAr and SNAr should never be denied, the DoM approach offers incontestable ortho regioselectivity, mild conditions, and perhaps most significantly, broad post-DoM synthetic potential. As a result, it has been called upon, with increasing favor and frequency, by

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

• group unmasks the aniline which undergoes nucleophilic aromatic substitution to introduce the pyrimidine system with the formation of 253. Methylation of the secondary amine function with methyl iodide prior to a second SNAr reaction with a sulfonamide-derived aniline affords pazopanib (Scheme 50) [76

• a nearby phenylalanine residue, whilst the trifluoromethyl group interacts with serine and arginine residues in a lipophilic pocket (Figure 8) [83]. In the discovery chemistry route [84] the heterocycle core was prepared from a SNAr reaction between chloropyrazine (276) and excess hydrazine

Perhalogenated pyrimidine scaffolds. Reactions of 5-chloro- 2,4,6-trifluoropyrimidine with nitrogen centred nucleophiles

• Emma L. Parks,
• Graham Sandford,
• John A. Christopher and
• David D. Miller

Beilstein J. Org. Chem. 2008, 4, No. 22, doi:10.3762/bjoc.4.22

• desirable process but one of the most difficult to achieve in practice. Pyrimidines are electron-deficient aromatic systems and, when halogenated, become very useful substrates for a variety of nucleophilic aromatic substitution (SNAr) processes [9] and, since numerous chloropyrimidines are commercially