Diels–Alder cycloadditions of N-arylpyrroles via aryne intermediates using diaryliodonium salts

• Huangguan Chen,
• Jianwei Han and
• Limin Wang

Beilstein J. Org. Chem. 2018, 14, 354–363, doi:10.3762/bjoc.14.23

• products under thermal conditions to afford arylamines [22]. Inspired by the pioneering work of Stuart and Wang [12][13], herein we reported the usage of diaryliodonium salts as aryne precursor for Diels–Alder cycloadditions of N-arylpyrroles (Scheme 1d). Results and Discussion We initially started the

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols

• Katrina Tait,
• Alysia Horvath,
• Nicolas Blanchard and
• William Tam

Beilstein J. Org. Chem. 2017, 13, 2888–2894, doi:10.3762/bjoc.13.281

• ], and cycloadditions using nitrile oxides to provide 15 and 16 [7]. In the literature, there are also many examples of the cleavage of the C–O bond of 3-aza-2-oxabicyclic alkenes 1 (Scheme 3). This includes the use of protic acid [8], using metal catalysts such as Pd [9], Fe or Cu [10], In [11

Preparation and isolation of isobenzofuran

• Morten K. Peters and
• Rainer Herges

Beilstein J. Org. Chem. 2017, 13, 2659–2662, doi:10.3762/bjoc.13.263

• (mp 20 °C) with a yield of 66%. The solid compound can be stored for up to 8 months at −15 °C without decomposition (polymerization). Conclusion Isobenzofuran (1) is one of the most reactive dienes in Diels–Alder reactions and other cycloadditions. For practical applications it has been generated and

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• intriguing versatility as building blocks in organic and medicinal chemistry, as their reactivity is unique. Their chemistry involves several highly selective reactions, e.g., [3 + 2] cycloadditions with azides and isoelectronic functional groups (among them the copper or ruthenium-catalyzed azide–alkyne

• -butylsulfinyl, R’ = Me, CHMe2, CH2CHMe2, cyclohexyl [17]. e,f) CuI or RuII-catalyzed [3 + 2] cycloadditions (CuAAC, RuAAC) [18][19][20][21]. e) R = Boc, R’ = Bn [19]. f) R = Boc, R’ = Me, CHMe2, CH2CHMe2, R’’ = Me, CHMe2, CH2Ph [21]. Two different approaches for the stereoselective de novo synthesis of

Solvent-free copper-catalyzed click chemistry for the synthesis of N-heterocyclic hybrids based on quinoline and 1,2,3-triazole

• Martina Tireli,
• Silvija Maračić,
• Stipe Lukin,
• Marina Juribašić Kulcsár,
• Dijana Žilić,
• Mario Cetina,
• Ivan Halasz,
• Silvana Raić-Malić and
• Krunoslav Užarević

Beilstein J. Org. Chem. 2017, 13, 2352–2363, doi:10.3762/bjoc.13.232

• bond bioisosteres made the click reaction a valuable synthetic methodology for conjugation of bioactive molecules [7][8][9] aiming to improve their biological activities [4][10][11]. Discovery of copper(I) ion catalysis in azide–alkyne cycloadditions was decisive for applications of this reaction, as

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• dicyanofumarates and maleates as highly functionalized electron-deficient dipolarophiles, dienophiles and Michael acceptors is summarized. The importance for the studies on reaction mechanisms of cycloadditions is demonstrated. Multistep reactions with 1,2-diamines and β-aminoalcohols leading to diverse five- and

• reactions with diazomethane albeit in very low yields [29]. [2 + 2]-Cycloadditions The electron-deficient dicyanofumarates E-1 react with electron-rich ethenes, yielding cyclobutane derivatives as product of [2 + 2]-cycloadditions. Depending on the reaction conditions and on the type of the electron-rich

• cyclobutanes 26 [20] (Scheme 7). The ratio of the isomers was the same irrespective of the configuration of 1b, indicating a stepwise reaction mechanism. Non-concerted [2 + 2]-cycloadditions were reported to occur between E- and Z-1b and bicyclo[2.1.0]pentene (27) [32]. Whereas in the case of E-1b two

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• reagents; (3) the elaboration of tandem and domino-processes utilizing conjugate addition of C-nucleophiles to nitrosoalkenes and finally, (4) the design of catalytic enantioselective versions of the Michael addition to nitrosoalkenes (for advances in catalytic asymmetric cycloadditions of nitrosoalkenes

A novel application of 2-silylated 1,3-dithiolanes for the synthesis of aryl/hetaryl-substituted ethenes and dibenzofulvenes

• Grzegorz Mlostoń,
• Paulina Pipiak,
• Róża Hamera-Fałdyga and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 1900–1906, doi:10.3762/bjoc.13.185

• presented protocol offers a new, highly efficient approach to tetrasubstituted ethenes and dibenzofulvenes bearing aryl and/or hetaryl substituents. Keywords: diazomethanes; 1,3-dipolar cycloadditions; olefination reactions; reaction mechanisms; thioketones; Introduction Aryl and hetaryl-substituted

• on [3 + 2]-cycloadditions with thioketones and diazo compounds, we turned our attention to hetaryl thioketones [18]. It turned out that the presence of the hetaryl groups strongly influences the reactivity of these dipolarophiles in reactions with diazomethane (CH2N2, Schönberg reaction) [19][20][21

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• heterocyclic terpenes by subsequent (hetero)-Diels–Alder or [4 + 1]-cycloadditions with nitrenes is also depicted. Keywords: dimerization; heterocycles; isoprene; monoterpene; palladium catalysis; Introduction The dimerization of conjugated dienes represents a useful, highly atom economic and straightforward

• that are used as alkyd coatings and perfume additives [39][40]. In addition, further functionalization reactions of the isoprene dimers can be carried out. In this work, we envisioned the synthesis of various heterocycles by (hetero)Diels–Alder and [4 + 1]-cycloadditions with nitrenes with the obtained

Synthesis and metal binding properties of N-alkylcarboxyspiropyrans

• Alexis Perry and
• Christina J. Kousseff

Beilstein J. Org. Chem. 2017, 13, 1542–1550, doi:10.3762/bjoc.13.154

• previously reported [28]. Presumably, this reaction proceeds via azomethine ylid 6 (Scheme 3); analogous indolium ylids have been used synthetically in 1,3-dipolar cycloadditions [29] and mechanistic studies have been published on the related decarboxylation of pyridinium 2-carboxylates [30]. Fortunately, α

Switchable highly regioselective synthesis of 3,4-dihydroquinoxalin-2(1H)ones from o-phenylenediamines and aroylpyruvates

• Juraj Dobiaš,
• Marek Ondruš,
• Gabriela Addová and
• Andrej Boháč

Beilstein J. Org. Chem. 2017, 13, 1350–1360, doi:10.3762/bjoc.13.132

• cycloadditions performed by p-TsOH (Table 1, column 4). From the above experimental results, we have proved that the regioselectivity of the cyclocondensation depends on both (a) the different nucleophilicity of the two amines from o-phenylenediamines 11a–f and (b) the electrophilicity of the α-carbonyl in 12a

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• conditions were feasible for the synthesis of glycosyl azides which are highly useful precursors for N-linked glycans [95] or Cu-catalyzed cycloadditions with alkynes (as shown above) [85]. By using tetrabutylammonium chloride and an amine base the highly reactive chlorinated intermediate forms that can be

Ultrasound-promoted organocatalytic enamine–azide [3 + 2] cycloaddition reactions for the synthesis of ((arylselanyl)phenyl-1H-1,2,3-triazol-4-yl)ketones

• Gabriel P. Costa,
• Natália Seus,
• Juliano A. Roehrs,
• Raquel G. Jacob,
• Ricardo F. Schumacher,
• Thiago Barcellos,
• Rafael Luque and
• Diego Alves

Beilstein J. Org. Chem. 2017, 13, 694–702, doi:10.3762/bjoc.13.68

• short reaction times. In addition, this protocol was extended to β-keto esters, β-keto amides and α-cyano ketones. Selanyltriazoyl carboxylates, carboxamides and carbonitriles were synthesized in high yields at short times of reaction under very mild reaction conditions. Keywords: cycloadditions

• have been used for this cycloaddition reaction [20][21][22][23][24][25][26][27][28][29]. Organocatalytic approaches based on β-enamine–azide or enolate–azide cycloadditions have been employed to synthesize 1,2,3-triazole scaffolds [30][31][32]. Depending on the organocatalyst employed, different

• carbonyl compounds could successfully generate an enamine or an enolate, and these species react as dipolarophiles with organic azides in organocatalyzed 1,3-dipolar cycloadditions. Our research group has demonstrated β-enamine–azide cycloaddition reactions for the synthesis of selenium-functionalized

Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

• Abdusalom A. Suleymanov,
• Dmitry V. Vasilyev,
• Valentin V. Novikov,
• Yulia V. Nelyubina and
• Dmitry S. Perekalin

Beilstein J. Org. Chem. 2017, 13, 639–643, doi:10.3762/bjoc.13.62

• formation of meta/para-products of Diels–Alder reactions [28][29][30][31][32], linear/branched products of hydrovinylation reactions [33][34], [2 + 2] cycloadditions vs Alder-ene reactions [35], E/Z isomerizations of alkenes [36][37] and other processes [38][39][40][41][42]. Herein, we report the

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• intermediate, delocalized diradical species. The influence of selenium as a ‘heavy atom’ for stabilization of this intermediate has been emphasized. Keywords: 1,3-dipolar cycloadditions; reaction mechanisms; reactive intermediates; thiocarbonyl S-methanides; thioketones; Introduction Thiocarbonyl S

• mechanisms in [3 + 2]-cycloadditions have intensively been studied [16] and recently, a computational study on their appearance in reactions of substituted acetylenes with nitrile oxides has been published [17]. Experimental The Gaussian 09 program system was used for all calculations [18]. The M06-2X

Diastereoselective anodic hetero- and homo-coupling of menthol-, 8-methylmenthol- and 8-phenylmenthol-2-alkylmalonates

• Matthias C. Letzel,
• Hans J. Schäfer and
• Roland Fröhlich

Beilstein J. Org. Chem. 2017, 13, 33–42, doi:10.3762/bjoc.13.5

• as a chiral auxiliary [27] to control the stereochemistry in Diels–Alder reactions [28], [2 + 2]- and [3 + 2]-cycloadditions and asymmetric ene reactions [29]; furthermore, it has been applied in 1,4-cuprate additions [30], Grignard additions [31], in supramolecular chemistry [32] and in alkylation

Development of a continuous process for α-thio-β-chloroacrylamide synthesis with enhanced control of a cascade transformation

• Olga C. Dennehy,
• Valérie M. Y. Cacheux,
• Benjamin J. Deadman,
• Denis Lynch,
• Stuart G. Collins,
• Humphrey A. Moynihan and
• Anita R. Maguire

Beilstein J. Org. Chem. 2016, 12, 2511–2522, doi:10.3762/bjoc.12.246

• ] and 1,3-dipolar cycloadditions [6][7][8][9], and oxidation of the sulfide group [10][11][12] are among a wide array of transformations which have been successfully applied to these compounds (Scheme 1). In order to fully exploit the synthetic potential of these β-chloroacrylamides, however, a means of

Sydnone C-4 heteroarylation with an indolizine ring via Chichibabin indolizine synthesis

• Florin Albota,
• Mino R. Caira,
• Constantin Draghici,
• Florea Dumitrascu and
• Denisa E. Dumitrescu

Beilstein J. Org. Chem. 2016, 12, 2503–2510, doi:10.3762/bjoc.12.245

• products 12a–c with yields in the range of 41–52%. Bearing in mind that the formation of indolizines through Chichibabin synthesis and 1,3-dipolar cycloaddition reaction requires in both cases the formation of an intermediate pyridinium N-ylide, it is expected that in these cycloadditions a mixture of

Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent

• Kohei Koyanagi,
• Yoshinori Takashima,
• Takashi Nakamura,
• Hiroyasu Yamaguchi and
• Akira Harada

Beilstein J. Org. Chem. 2016, 12, 2495–2502, doi:10.3762/bjoc.12.244

• , including hydrolysis reactions [10][11][12][13][14][15], C–H bond activation [34][35][36], olefin epoxidation [37][38][39], Diels–Alder reactions [40][41][42], 1,3-dipole cycloadditions [43][44], and polymerizations [45][46][47], among others. Selective substrate recognition and activation are essential

Construction of bis-, tris- and tetrahydrazones by addition of azoalkenes to amines and ammonia

• Artem N. Semakin,
• Aleksandr O. Kokuev,
• Yulia V. Nelyubina,
• Alexey Yu. Sukhorukov,
• Petr A. Zhmurov,
• Sema L. Ioffe and
• Vladimir A. Tartakovsky

Beilstein J. Org. Chem. 2016, 12, 2471–2477, doi:10.3762/bjoc.12.241

• 1 to ammonia (Table 2) have a special significance because the expected trishydrazones 11 are obvious analogs of tris(iminomethyl)amines widely used in the catalysis of azide–alkyne cycloadditions [29][30][31][32][34]. Furthermore, intramolecular cyclotrimerization of C=N bonds in trishydrozones

A new paradigm for designing ring construction strategies for green organic synthesis: implications for the discovery of multicomponent reactions to build molecules containing a single ring

• John Andraos

Beilstein J. Org. Chem. 2016, 12, 2420–2442, doi:10.3762/bjoc.12.236

• - and 6-membered monocyclic rings are most commonly made by [2 + 2 + 1] and [3 + 2 + 1] cycloadditions where 57% and 76% of them, respectively, have a 100% chance of being intrinsically green from a design perspective. A survey of over 2000 MCRs used to synthesize specific types of heterocyclic rings

• consist algebraically of the same kinds of fragment elements; namely, two 2s and two 1s. The fourth entry in Figure 3 shows the visual distinction between partitioning a 6-membered ring via [2 + 2 + 1 + 1] and [2 + 1 + 2 + 1] cycloadditions. Similarly, [3 + 2 + 1 + 1] and [3 + 1 + 2 + 1] partitions for a

• strategies. The traditional mapping is shown in red and only 2 out of 18 novel mappings shown in blue have been reported recently. Scheme 10 shows the following literature examples of [3 + 2 + 1] cycloadditions following the traditional mapping (red structure shown in Figure 9): Biginelli [163][164][165

Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides

• Ilya V. Efimov,
• Marsel Z. Shafikov,
• Nikolai A. Beliaev,
• Natalia N. Volkova,
• Tetyana V. Beryozkina,
• Wim Dehaen,
• Zhijin Fan,
• Viktoria V. Grishko,
• Gert Lubec,
• Pavel A. Slepukhin and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2016, 12, 2390–2401, doi:10.3762/bjoc.12.233

• 4i), respectively. The regio- and stereospecificity and the apparent reaction rate increase by the introduction of electron-withdrawing substituents into the benzonitrile oxide structure, allow to presume that the reaction of enamines with nitrile oxides can be described as 1,3-dipolar cycloadditions

Stereoselective synthesis of fused tetrahydroquinazolines through one-pot double [3 + 2] dipolar cycloadditions followed by [5 + 1] annulation

• Xiaofeng Zhang,
• Kenny Pham,
• Shuai Liu,
• Marc Legris,
• Alex Muthengi,
• Jerry P. Jasinski and
• Wei Zhang

Beilstein J. Org. Chem. 2016, 12, 2204–2210, doi:10.3762/bjoc.12.211

• using one-pot intermolecular or intramolecular [3 + 2] azomethine ylide cycloadditions [22][23][24][25][26][27] as the initial step followed by cyclization or cycloaddition reactions to form polycyclic scaffolds with skeleton, substitution, and stereochemistry diversities. Introduced in this paper is a

• , potassium channel, mPGES-1, and tubulin inhibitors, as well as the immunomodulatory drug thalidomide [28][29][30][31][32] (Figure 1). Results and Discussion Our initial effort was focused on the development of reaction conditions for the one-pot double [3 + 2] cycloadditions. The first [3 + 2] cycloaddition

• . Upon the completion of the reaction as monitored by LC–MS, the reaction mixture was concentrated and then isolated on a semi-preparative HPLC with a C18 column to afford purified product 1. Heterocyclic fragments in bioactive compounds. One-pot double [3 + 2] cycloadditions and denitrogenation for

Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

• Ángel Cantín,
• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188, doi:10.3762/bjoc.12.208

• selectivity and atom economy. Moreover, Diels–Alder cycloadditions in combination with heterogeneous catalysts (i.e. doped-microporous materials) represent an interesting approach for the conversion of biomass feedstock into stable chemicals such as furfural derivatives, platform molecules which can be

• Diels–Alder reaction selectivity [28]. The DAR of cyclopentadiene with p-benzoquinone is a well-known example of cycloadditions, and some results can be found on the control of the selectivity to the different isomers. In homogeneous phase, equimolar amounts of diene and dienophile afford two isomers

The direct oxidative diene cyclization and related reactions in natural product synthesis

• Juliane Adrian,
• Leona J. Gross and
• Christian B. W. Stark

Beilstein J. Org. Chem. 2016, 12, 2104–2123, doi:10.3762/bjoc.12.200

• , it was finally broadly accepted that the overall reaction is a result of two consecutive syn-stereospecific [3 + 2]-oxidative cycloadditions (cf. type A mechanism; Scheme 3) [9][10][11]. Therefore, the double bond geometry of each of the two reacting double bonds translates directly to the relative