Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• Materiais Inorgânicos, Universidade Federal de Santa Maria, 97105-900, Santa Maria, Rio Grande do Sul, RS, Brazil 10.3762/bjoc.9.96 Abstract Chiral nonracemic aminated nitroso acetals were synthesized via diastereoselective multicomponent [4 + 2]/[3 + 2] cycloadditions employing new (S,E)-γ-nitrogenated

• furnish cyclic nitronate derivatives of type 3 [1][3]. In particular, the reactivity of nitroalkenes with unactivated olefins has been extensively investigated by Denmark and co-workers in [4 + 2] hetero-Diels–Alder (HDA) cycloadditions [1][3] and, in some instances, the resulting cyclic nitronates such

• -dipolarophiles to furnish nitroso acetals of type 4 in an inter- or intramolecular fashion [1][2][3][8][9]. These nitroso acetals can be transformed into functionalized pyrrolizidin-3-ones and in sequence into alkaloid nuclei [1][3][10][11]. The majority of the tandem nitroalkene cycloadditions require the

Caryolene-forming carbocation rearrangements

• Quynh Nhu N. Nguyen and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2013, 9, 323–331, doi:10.3762/bjoc.9.37

• a hydrogen-bridged minimum. Both mechanisms are predicted to involve concerted suprafacial/suprafacial [2 + 2] cycloadditions, whose asynchronicity allows them to avoid the constraints of orbital symmetry. Keywords: carbocation; cycloaddition; density functional theory; mechanism; reactive

Towards a biocompatible artificial lung: Covalent functionalization of poly(4-methylpent-1-ene) (TPX) with cRGD pentapeptide

• Lena Möller,
• Christian Hess,
• Jiří Paleček,
• Yi Su,
• Axel Haverich,
• Andreas Kirschning and
• Gerald Dräger

Beilstein J. Org. Chem. 2013, 9, 270–277, doi:10.3762/bjoc.9.33

• required for these kinds of 1,3-dipolar cycloadditions, but their potential cytotoxic properties limit the usability in biomedical applications [16][17]. For overcoming this problem, several copper-free ligation methods were developed. In this work we pursue both options, i.e., the copper-mediated as well

• , by the use of Huisgen-type “click” chemistry (Scheme 2). cRGD pentapeptide 1b was prepared in sufficient amounts by solution-phase chemistry [23]. Because of the disadvantage associated with copper-mediated 1,3-cycloadditions of alkynes with azides in biological or biomedical applications we

• cycloadditions, the model compound fluoresceinyl azide 9[29][30] was first coupled to TPX derivatives 7a or 7b, under identical conditions as described for cRGD peptide 1b. The resulting polymers 8c and 8d were studied by determining the UV absorption peaks of fluorescein between 400 and 600 nm (Figure 4

Peptoids and polyamines going sweet: Modular synthesis of glycosylated peptoids and polyamines using click chemistry

• Daniel Fürniss,
• Timo Mack,
• Frank Hahn,
• Sidonie B. L. Vollrath,
• Katarzyna Koroniak,
• Ute Schepers and
• Stefan Bräse

Beilstein J. Org. Chem. 2013, 9, 56–63, doi:10.3762/bjoc.9.7

• azide alkyne cycloadditions. In addition, the up-scaling of some particular azide-modified sugars is described. Keywords: click chemistry; glycans; peptoids; polyalkynes; polyamines; solid-phase chemistry; Introduction To date, oligosaccharides have gained more and more interest as potential drugs in

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• years. This also presented an opportunity to compare different reactor types in areas such as selectivity, yield and productivity [22]. Review Microflow photochemistry Photocycloadditions Although many photocycloadditions have been performed by using other types of reactor, only [2 + 2] cycloadditions

• ) [26]. Asymmetric induction can be achieved in [2 + 2] cycloadditions through the use of a chiral auxilliary. The [2 + 2] reaction shown in Scheme 3 employed a chiral ester function to direct the facial selectivity of the addition of the enone to cyclopentene. Diastereoselectivity was found to be

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• steps (high step economy). Keywords: alicyclic; bisallenes; cyclic; cycloadditions; cycloisomerization; isomerization; molecular complexity; step economy; Table of Contents Introduction Review Acyclic conjugated bisallenes 1.1 Synthesis of hydrocarbons 1.2 Synthesis of functionalized systems 1.3

• the 2-azetidinone 113 carrying the 1,2,4,5-hexatetraen-3-yl substituent in the 4-position. The bisallene is a very good diene for Diels–Alder cycloadditions as will be discussed in Section 1.4.1. The unusual hexakis(ferrocenyl)-1,2,4,5-hexatetraene (116) is produced as one of many side-products when

• : “internally” 2 possesses a conjugated diene system and “externally” it displays two cumulated ones. For the case of cycloadditions (see below) this should allow for [2 + 4] (Diels–Alder) and [2 + 2]cycloadditions (additions to allenes, ketenes, etc.). As we shall see later, both modes of cycloadditions have

Asymmetric Brønsted acid-catalyzed aza-Diels–Alder reaction of cyclic C-acylimines with cyclopentadiene

• Magnus Rueping and
• Sadiya Raja

Beilstein J. Org. Chem. 2012, 8, 1819–1824, doi:10.3762/bjoc.8.208

• diastereoselectivities under mild reaction conditions. The results reported not only show that chiral BINOL derived phosphoric acid diesters can be efficient catalysts for [4 + 2] cycloadditions involving less-electron-rich dienes but additionally demonstrate the high potential of these acidic Brønsted acids in

Copper-catalyzed CuAAC/intramolecular C–H arylation sequence: Synthesis of annulated 1,2,3-triazoles

• Rajkumar Jeyachandran,
• Harish Kumar Potukuchi and
• Lutz Ackermann

Beilstein J. Org. Chem. 2012, 8, 1771–1777, doi:10.3762/bjoc.8.202

• -economical syntheses of annulated 1,2,3-triazoles were accomplished through copper-catalyzed intramolecular direct arylations in sustainable one-pot reactions. Thus, catalyzed cascade reactions involving [3 + 2]-azide–alkyne cycloadditions (CuAAC) and C–H bond functionalizations provided direct access to

• consisting of copper(I)-catalyzed [3 + 2]-azide–alkyne cycloadditions (CuAAC) and intramolecular C–H bond arylations. Notably, the optimized copper catalyst accelerated two mechanistically distinct transformations, which set the stage for the formation of up to one C–C and three C–N bonds in a chemo- and

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

• Andrew Tigchelaar and
• William Tam

Beilstein J. Org. Chem. 2012, 8, 1765–1770, doi:10.3762/bjoc.8.201

• Andrew Tigchelaar William Tam Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1 10.3762/bjoc.8.201 Abstract Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl

• –94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium catalyst. Keywords: alkynyl halide; cycloaddition; diene-tethered alkyne; iridium; transition-metal catalyst; Introduction Iridium complexes have been used as catalysts for a wide variety of reactions

• , including homogeneous hydrogenation [1][2], C–H activation [3][4][5], asymmetric ring-opening reactions [6], and a variety of cycloisomerizations [7][8][9][10], and cycloadditions [11][12][13][14][15][16][17][18][19][20]. Traditionally these types of cycloisomerization and cycloaddition reactions are

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• FLPs [35], Mδ+═Eδ− FLPs may also react with nonpolar unsaturated substrates, such as alkenes or alkynes, by polarizing the substrate to facilitate cycloaddition. [2 + 2] cycloadditions of Mδ+═Eδ− FLPs with alkenes/alkynes have been thoroughly explored in the context of olefin metathesis (where E = CR2

Approaches to α-amino acids via rearrangement to electron-deficient nitrogen: Beckmann and Hofmann rearrangements of appropriate carboxyl-protected substrates

• Sosale Chandrasekhar and
• V. Mohana Rao

Beilstein J. Org. Chem. 2012, 8, 1393–1399, doi:10.3762/bjoc.8.161

• be investigated (most notably the Strecker reaction) [2], but recent developments focus on cycloadditions [3], rare amino acids [4], chiral catalysis [5], etc. It is noteworthy, however, that two of the most widely applied methods for the introduction of the amine group – the Beckmann [6][7][8][9

Palladium-catalyzed substitution of (coumarinyl)methyl acetates with C-, N-, and S-nucleophiles

• Kalicharan Chattopadhyay,
• Erik Fenster,
• Alexander J. Grenning and
• Jon A. Tunge

Beilstein J. Org. Chem. 2012, 8, 1200–1207, doi:10.3762/bjoc.8.133

• ]. Due to the ambiphilic nature of the heterocyclic ring of coumarin, this core-structure undergoes a diverse array of coupling reactions, such as halogenations [25], cycloadditions [26][27][28][29][30][31][32], conjugate additions [33][34][35][36][37] and transition-metal-catalyzed C–H activation

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

• predictability of their potency and selectivity as inhibitors is still limited. We have recently reported the synthesis of triazole-based α-helix mimetics 3 and 4 [16], which are efficiently available through azide–alkyne cycloadditions [17]. We now report the use of this chemistry to prepare libraries of

• –t and either copper or ruthenium-catalyzed [2 + 3] cycloadditions. The three reactions and the obtained products 11 (reaction 1), 12 (reaction 2) and 13 (reaction 3) are summarized in Table 2. Reaction 1 follows the established protocol and, gave after removal of the copper salts with a solution of

• , DMSO-d6). Compounds 13, with the exception of compound 13f, were only characterized by mass spectrometry during the synthesis of the compound library. The copper-mediated [2 + 3] cycloadditions are restricted to terminal alkynes. However, the ruthenium-catalysis allows the use of internal alkynes. In

Parallel and four-step synthesis of natural-product-inspired scaffolds through modular assembly and divergent cyclization

• Hiroki Oguri,
• Haruki Mizoguchi,
• Hideaki Oikawa,
• Aki Ishiyama,
• Masato Iwatsuki,
• Kazuhiko Otoguro and
• Satoshi Ōmura

Beilstein J. Org. Chem. 2012, 8, 930–940, doi:10.3762/bjoc.8.105

• cycloadditions with the dipolarophiles installed at modules 3 and 4 leading to either tetracyclic 14 or hexacyclic 13. In this full account, we also employ a piperidine-based manifold 15 bearing an amino group in order to expand the applicability of the various building blocks in the four-step parallel synthesis

• scaffold. In addition, removal of the N-nosyl protecting group by treatment with benzenethiol led to 26b in quantitative yield [42]. To generate skeletal variations by altering the sites of the cycloadditions, we next synthesized a branched precursor 29 bearing a pair of identical indole units at modules 3

• the cycloadditions efficiently incorporated consecutive quaternary centers into the complex fused skeleton, overriding the considerable steric hindrance of the dipolarophiles composed of the tri- and even tetra-substituted olefin groups. To test the generality of the site-selective cycloaddition at

An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

• Zhiyuan Ma,
• Feng Ni,
• Grace H. C. Woo,
• Sie-Mun Lo,
• Philip M. Roveto,
• Scott E. Schaus and
• John K. Snyder

Beilstein J. Org. Chem. 2012, 8, 829–840, doi:10.3762/bjoc.8.93

• Intramolecular inverse electron demand cycloadditions of isatin-derived 1,2,4-triazines with acetylenic dienophiles tethered by amidations or transesterifications proceed in excellent yields to produce lactam- or lactone-fused α-carbolines. Beginning with various isatins and alkynyl dienophiles, a pilot-scale

• are also known [62][63][64]. In addition, cycloadditions of 3-vinyl-7-azaindole have also been used to close the pyridine ring [65], as have intramolecular dipolar cycloadditions of 2-azidoindole derivatives [66], and intramolecular cycloadditions of carbodiimides [67][68]. We had envisioned that a

• library of annulated α-carboline structures 6 could be prepared by the intramolecular inverse electron demand Diels–Alder reaction (IEDDA) of isatin-derived 1,2,4-triazines 7 with tethered electron-rich dienophiles (Scheme 1) [69]. Inverse electron demand Diels–Alder cycloadditions employing electron

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

• Marcin Jasiński,
• Dieter Lentz and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

• diiodide; Introduction During the last few decades carbohydrate-derived nitrones have turned out to be particularly attractive tools for the synthesis of structurally complex compounds [1][2][3][4]. Employed mainly as 1,3-dipoles in cycloadditions [5][6] or as imine analogues in nucleophilic additions [7

• been introduced and broadly studied by Vasella and co-workers [14][15][16][17][18][19][20] and has also been used by other groups [21][22][23][24][25]. They observed moderate to high diastereoselectivities for 1,3-dipolar cycloadditions and for nucleophilic additions. Successful applications of these

Alkoxide-induced ring opening of bicyclic 2-vinylcyclobutanones: A convenient synthesis of 2-vinyl-substituted 3-cycloalkene-1-carboxylic acid esters

• Xiufang Ji,
• Zhiming Li,
• Quanrui Wang and
• Andreas Goeke

Beilstein J. Org. Chem. 2012, 8, 650–657, doi:10.3762/bjoc.8.72

• rings, the substitution pattern on the ring, and the properties of the reagents as well as the reaction conditions. In particular, the ring opening of certain fused-ring cyclobutanones, which are easily prepared by the well-established [2 + 2] cycloadditions of ketenes with various cycloalkenes, has

• cycloadditions proceeded with complete regio- and stereoselectivity with respect to the olefin 1, but less so with respect to the ketene 3 (Table 1), such that endo-4 and exo-4 isomers were formed in variable amounts, depending on the nature of the substrates. In general, the conversions of cyclopenta-1,3-diene

Aryl nitrile oxide cycloaddition reactions in the presence of pinacol boronic acid ester

• Sarah L. Harding,
• Sebastian M. Marcuccio and
• G. Paul Savage

Beilstein J. Org. Chem. 2012, 8, 606–612, doi:10.3762/bjoc.8.67

• favouring the oxidation of carbon–boron bonds, which makes boronic ester chemistry chemoselective, is a constraint that potentially limits the utility of nitrile oxide cycloadditions in the presence of a boronic acid ester. 4-Formylphenylboronic acid pinacol ester 4 is commercially available or easily

• detected. We have previously observed that nitrile oxide cycloadditions to this hydantoin and related compounds can show facial selectivity based on atropisomerism around the N-aryl bond [38][44]. With benzonitrile oxide the facial selectivity was 30:1 favouring addition anti to the tert-butyl group

Stereoselective, nitro-Mannich/lactamisation cascades for the direct synthesis of heavily decorated 5-nitropiperidin-2-ones and related heterocycles

• Pavol Jakubec,
• Dane M. Cockfield,
• Madeleine Helliwell,
• James Raftery and
• Darren J. Dixon

Beilstein J. Org. Chem. 2012, 8, 567–578, doi:10.3762/bjoc.8.64

• ]. Arguably the most general route employs cycloadditions and subsequent manipulation of the partially unsaturated ring system [49][50][51][52][53]. We believed a powerful entry to piperidine rings and related heterocyclic structures could employ a nitro-Mannich/lactamisation cascade of γ-nitro ester starting

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

• Rob De Vreese and
• Matthias D’hooghe

Beilstein J. Org. Chem. 2012, 8, 398–402, doi:10.3762/bjoc.8.43

• -lactam to γ-lactam ring expansions [29][30], aziridine ring openings followed by cyclization with enolates [31], palladium-catalyzed cyclizations [32], cycloadditions [33], multicomponent reactions [34], and even NHC catalysis [35][36]. Nevertheless, the methodology developed by Rovis indisputably

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• bicyclic isomers 20 (Scheme 5) [79][88]. The reluctance to form the bicyclic isomer dictates the reactivity of azepines, as they exhibit the characteristics of cyclic polyene chemistry, which is illustrated by the ability of the monocyclic isomer to undergo cycloadditions as a 2π (→21) [89], 4π (→22) [84

• + 2] cycloadditions of the in situ generated singlet phosphinidene 35 with olefins or acetylenes (Scheme 7) [5][6][7][8][9]. This approach has even lead to the detection of the transient phosphinidene species by employing electrospray ionization tandem mass spectrometry (ESIMS/MS); its gas-phase

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

• azomethine imines. Intramolecular 1,3-dipolar cycloadditions of sydnone derivatives have not been as thoroughly investigated, and so far only a few examples are known [18][19][20]. Photochemically induced intramolecular 1,3-dipolar cycloadditions have been studied on 3,4-disubstituted sydnone derivatives [18

• . Illustration of intramolecular [3 + 2] cycloadditions. Styryl-sydnone 1 and stilbenyl sydnone 2 and their photoproducts F and G, respectively; target molecules 3 in this work. ORTEP of compound 14. Proposed stereochemical pathway of sydnone ring (CH–N) and trans- and cis-stilbene (α–β). Proposed stereochemical

Highly efficient cyclosarin degradation mediated by a β-cyclodextrin derivative containing an oxime-derived substituent

• Michael Zengerle,
• Florian Brandhuber,
• Christian Schneider,
• Franz Worek,
• Georg Reiter and
• Stefan Kubik

Beilstein J. Org. Chem. 2011, 7, 1543–1554, doi:10.3762/bjoc.7.182

• (“click-reaction”) [33] from mono-6-azido-6-deoxy-β-cyclodextrin (4) and a functionalized alkyne (Scheme 3, route B). Conjugations by copper(I)-catalyzed azide–alkyne cycloadditions have become popular in many different fields of chemistry [33][34], including cyclodextrin chemistry [35][36][37][38][39][40

Multistep flow synthesis of vinyl azides and their use in the copper-catalyzed Huisgen-type cycloaddition under inductive-heating conditions

• Lukas Kupracz,
• Jan Hartwig,
• Jens Wegner,
• Sascha Ceylan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2011, 7, 1441–1448, doi:10.3762/bjoc.7.168

• -type cycloadditions The copper-catalyzed Huisgen-type cycloaddition (CuAAC) is a general and useful method for the synthesis of 1,4-disubstituted-1,2,3-triazoles and is based on the 1,3-dipolar cycloaddition of alkynes and azides [28]. Besides Cu(I) sources also Cu(0) sources, such as copper wire [29

Ugi post-condensation copper-triggered oxidative cascade towards pyrazoles

• Aurélie Dos Santos,
• Laurent El Kaim,
• Laurence Grimaud and
• Caroline Ronsseray

Beilstein J. Org. Chem. 2011, 7, 1310–1314, doi:10.3762/bjoc.7.153

• advantage of the functional group tolerance of the Ugi coupling to apply to these adducts the various cyclizations offered by the chemists toolkit. We became involved in the Ugi-post-condensation field through our initial interest in radical processes. We found that, compared with classical cycloadditions