Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• release approach, the Xiao group reported a synthesis of the pyrroles 35.3 in 2014 [153]. They can be accessed via a photocatalytic formal [3 + 2] cycloaddition of the 2H-azirines 35.1 and the alkynes 35.2 (Scheme 35). The use of Mes-Acr-Me+ (OD2) was successful due to its high reduction potential in the

Synthesis of esters of diaminotruxillic bis-amino acids by Pd-mediated photocycloaddition of analogs of the Kaede protein chromophore

• Esteban P. Urriolabeitia,
• Pablo Sánchez,
• Alexandra Pop,
• Cristian Silvestru,
• Eduardo Laga,
• Ana I. Jiménez and
• Carlos Cativiela

Beilstein J. Org. Chem. 2020, 16, 1111–1123, doi:10.3762/bjoc.16.98

• , harsh irradiation conditions and low yields) [16][20], or (b) the direct [2 + 2] cycloaddition does not take place and it is necessary to synthesize a cyclobutane precursor and then functionalize it, thus increasing the number of reaction steps, the waste material, and decreasing the global yield [16

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• photoinduced cycloaddition of carbon dioxide with epoxides [56]. The synthesis of a 3D supramolecular framework, [{Mn(TCPP)0.5(H2O)}·2H2O]n, where Mn(TCPP) is Mn(II) meso-tetrakis(4-carboxyphenyl)porphyrin, was derived from MnCl2·6H2O and TCPP. The cycloaddition product, a cyclic carbonate, was obtained from

• (Scheme 26) [61][67][68]. In this section, both reactions are presented and discussed. Singlet oxygen in pericyclic reactions Many important organic transformations can be performed by singlet oxygen including ene, [2 + 2] and [4 + 2] cycloaddition reactions for the formation of hydroperoxides, dioxetanes

• concerted) are still ongoing. The generally accepted mechanisms for these reactions are shown in Scheme 27, and propose a stepwise mechanism for ene and [2 + 2] cycloaddition, and a concerted mechanism for [4 + 2] cycloaddition [67]. In this part of the review, we decided to highlight the historically

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• the 2-phospholene derivatives is beneficial for having enhanced organocatalytic activity, in a few instances [47]. The McCormack cycloaddition is a key reaction for the preparation of the five-membered P-heterocyclic scaffold, as both the 2- or 3-phospholene core can be prepared depending on the

• calculations, and the results justified why a given isomerization pathway leads to an equilibrium or proceeds until completion. McCormack cycloaddition is still an established method for the synthesis of both 2- or 3-phospholene oxides. However, our paper outlined that the preparation of 2-phospholene oxide

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• subsequent Eu(fod)3-catalyzed intermolecular Diels–Alder cycloaddition and epoxidation reactions (Scheme 5) [69]. In this stereoselective synthesis, the last biomimetic step was critical to obtain the proper enantiomer of the tetracyclic core of nanolobatolide. Amphidinolide macrolides Amphidinolides

• on a Diels–Alder cycloaddition, an intramolecular Mitsunobu reaction, a [3,3]-sigmatropic rearrangement, and a ring-closing metathesis. As an alternative to this approach, Clark et al. [86] efficiently performed a sequential Ru-catalyzed enyne metathesis in combination with a hydroboration, and an

• subunit, including Diels–Alder cycloaddition and advanced functionalization reactions, gave access to manzamine A and E. Rhodexin A Jung et al. [87][88][89] succeeded in the stereoselective synthesis of rhodexin A (17), a steroid with potent cardiotonic properties and with activity against human leukemia

Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes

• Zeguo Fang,
• Nawaf Al-Maharik,
• Peer Kirsch,
• Matthias Bremer,
• Alexandra M. Z. Slawin and
• David O’Hagan

Beilstein J. Org. Chem. 2020, 16, 674–680, doi:10.3762/bjoc.16.65

• illustrated in Scheme 1. Difluorocyclopropane 8 can be directly prepared through a [2 + 1] carbene cycloaddition reaction. Thus, treatment of 12 with trimethyl(trifluoromethyl)silane (TMSCF3) and sodium iodide under refluxing conditions [13][14] gave the corresponding product 8 in one step and a 55% yield

Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties

• Takahide Shimada,
• Shigeki Mori,
• Masatoshi Ishida and
• Hiroyuki Furuta

Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53

• -tethered BODIPY derivatives serve as a substrate in the copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction, which is known as “click” reaction, allowing for a biological tissue labelling [35][36]. In addition, ethynyl-substituted BODIPYs yield unique π-conjugated BODIPY-based macrocycles by

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• employed procedures for the creation of triazole products is the Huisgen azide–alkyne cycloaddition, and the reaction selectively forms one type of triazole products. Many of the alkyne and azide substrates are commercially available, many others can easily be prepared with a good range of functional

• reactions that are stereospecific, high-yielding, modular, wide in scope, executable under simple reaction conditions, conductable in safe or easily removable solvents, and that generate only nonoffensive byproducts. Of course, the classical Huisgen 1,3-dipolar cycloaddition does not fit into the above

• definition and fails as a real “click” reaction. Although this cyclization reaction requires elevated temperatures and often yields both the 1,4- and 1,5-regioisomers, the Cu or Ru alkyne–azide cycloaddition falls exactly into the above definition [11]. In this respect, the copper-catalyzed cycloaddition

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• area, reporting on the synthesis of the first heteroleptic bis-NHC and mixed NHC/phosphine copper(I) complexes [20][21][22]. Interestingly, these new copper-based complexes have shown excellent activity in the [3 + 2] cycloaddition reaction of azides/sulfonyl azides and alkynes (Scheme 1, right) [22

• diphenylamine, only 20% of the desired product was observed (12c). Interestingly, with benzyl azide, a substrate not containing a sulfonyl moiety, the product obtained is the 1,2,3-triazole derivative [33], resulting from a [3 + 2] cycloaddition of azide and alkyne (Scheme 6). The catalytic system was also

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• alkyne–azide cycloaddition reaction has been applied successfully to prepare click-phosphine ligands [72]. The presence of three nitrogen atoms within the five-membered ring results in a high activation of the α-position and the highly acidic nature of the proton makes it easy for abstraction. Sharpless

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• , Viale Morgagni 85, 50134 Florence, Italy 10.3762/bjoc.16.23 Abstract The Cu-catalyzed multicomponent ketone–amine–alkyne (KA2) reaction was combined with a Pauson–Khand cycloaddition to give access of unprecedented constrained spirocyclic pyrrolocyclopentenone derivatives following a DOS couple-pair

• [39][40], consisting of a [2 + 2 + 1] cycloaddition between an olefin, alkyne, and carbon monoxide. This reaction has been also applied in cascade approaches [41], and in combination with RCM [42], Diels–Alder [43] and Staudinger [44] reactions to produce novel structurally complex chemical entities

• . Following our interest to DOS as a synthetic strategy for the generation of molecular scaffolds according to a couple/pair approach [45][46][47], we reasoned to combine the copper-catalyzed ketone–amine–alkyne (KA2) multicomponent coupling reaction [48] with the Pauson–Khand cycloaddition as the pairing

The use of isoxazoline and isoxazole scaffolding in the design of novel thiourea and amide liquid-crystalline compounds

• Itamar L. Gonçalves,
• Rafaela R. da Rosa,
• Vera L. Eifler-Lima and
• Aloir A. Merlo

Beilstein J. Org. Chem. 2020, 16, 175–184, doi:10.3762/bjoc.16.20

• , 8, 9, 12 and 13 were then prepared by [3 + 2]-1,3-dipolar cycloaddition of nitrile oxide (ArCNO) formed in situ from oximes and a number of alkenes as dipolarophiles, to yield the precursors of the cycloadducts isoxazolines 2, 7 and 11 regioselectively. The cycloadducts were subjected to SnCl2

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• electrocyclization or E-to-Z isomerization reactions, whereas the well-established photochromic cycloaddition–cycloreversion equilibrium to establish photoswitchable DNA binders has so far been widely neglected. In fact, there is only one reported example for the use of the reversible photoinduced dimerization of

• derivative 3b gave the corresponding cycloaddition product much faster, i.e., within a few minutes under these conditions, and the formation of the corresponding Z-isomer proceeded only to a marginal extent. In aqueous solution, the substrates 3a–d showed essentially the same photochemical behavior, however

Influence of the cis/trans configuration on the supramolecular aggregation of aryltriazoles

• Sara Tejera,
• Giada Caniglia,
• Rosa L. Dorta,
• Andrea Favero,
• Javier González-Platas and
• Jesús T. Vázquez

Beilstein J. Org. Chem. 2019, 15, 2881–2888, doi:10.3762/bjoc.15.282

• supramolecular studies and report herein the ability of ditriazoles to form gels, their physical properties, as well as the dependence of these properties on the cis/trans relative configuration. Results and Discussion A large set of mono- and ditriazoles was synthesized using cycloaddition reactions based on

Diversity-oriented synthesis of spirothiazolidinediones and their biological evaluation

• Sambasivarao Kotha,
• Gaddamedi Sreevani,
• Lilya U. Dzhemileva,
• Milyausha M. Yunusbaeva,
• Usein M. Dzhemilev and
• Vladimir A. D’yakonov

Beilstein J. Org. Chem. 2019, 15, 2774–2781, doi:10.3762/bjoc.15.269

• inducers in the HeLa, Hek293, U937, Jurkat, and K562 cell lines. Keywords: apoptosis; biologically active; [2 + 2 + 2] cycloaddition; flow cytometry; spiro thiazolidinedione; Introduction Heterocyclic compounds play a vital role in the metabolism of all living cells. Thus, most of the biologically active

• generate new derivatives suitable for the multiple interaction sites. Further, the antitumour activity of these compounds were studied. Therefore, we synthesized the required diyne derivatives of thiazolidinedione for [2 + 2 + 2] cycloaddition, in the presence of propargyl bromide and K2CO3 in DMF. The

• dipropargyl derivatives 7e and 7f were then treated with different propargyl alcohols 16 in the presence of Wilkinson’s catalyst/Ti(OiPr)4 under ethanol reflux conditions [53] to obtain the corresponding [2 + 2 + 2] cyclotrimerized alcohols 17–19 and 21 in good yields. During the [2 + 2 + 2] cycloaddition of

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

• Valentina A. Ol’shevskaya,
• Elena G. Kononova and
• Andrei V. Zaitsev

Beilstein J. Org. Chem. 2019, 15, 2704–2709, doi:10.3762/bjoc.15.263

• 1,2,3-triazole heterocycles via the copper-catalyzed azide–alkyne cycloaddition reaction (CuAAC) between alkynes and azides, developed independently by Sharpless [41] and Meldal [42]. In addition to the applications of triazoles as pharmacophores in the potential biologically active molecules, these

Unexpected one-pot formation of the 1H-6a,8a-epiminotricyclopenta[a,c,e][8]annulene system from cyclopentanone, ammonia and dimethyl fumarate. Synthesis of highly strained polycyclic nitroxide and EPR study

• Sergey A. Dobrynin,
• Igor A. Kirilyuk,
• Yuri V. Gatilov,
• Andrey A. Kuzhelev,
• Olesya A. Krumkacheva,
• Matvey V. Fedin,
• Michael K. Bowman and
• Elena G. Bagryanskaya

Beilstein J. Org. Chem. 2019, 15, 2664–2670, doi:10.3762/bjoc.15.259

• observed in a one-pot synthesis from cyclopentanone, dimethyl fumarate and ammonium acetate. This multistep reaction includes 1,3-dipolar cycloaddition of dimethyl fumarate to the cyclic azomethine ylide formed in situ from cyclopentanone and ammonia. The polycyclic amine product was easily converted into

• nitroxide [4]. Here we report the unexpected formation of a highly strained polycyclic amine from cyclopentanone, dimethyl fumarate and ammonium acetate. This multistep reaction obviously includes the 1,3-dipolar cycloaddition of dimethyl fumarate with cyclic azomethine ylide formed in situ from

• heterocycle formation [11]. Presumably, a prototropic shift in the enamine-imine intermediate 4 is followed by electrocyclization to the cyclic azomethine ylide, which then reacts with dimethyl fumarate in a 1,3-dipolar cycloaddition. The suggested mechanism accounts for the trans-position of the methyne

AgNTf₂-catalyzed formal [3 + 2] cycloaddition of ynamides with unprotected isoxazol-5-amines: efficient access to functionalized 5-amino-1H-pyrrole-3-carboxamide derivatives

• Ziping Cao,
• Jiekun Zhu,
• Li Liu,
• Yuanling Pang,
• Laijin Tian,
• Xuejun Sun and
• Xin Meng

Beilstein J. Org. Chem. 2019, 15, 2623–2630, doi:10.3762/bjoc.15.255

• Analysis, Qufu 273165, P. R. China 10.3762/bjoc.15.255 Abstract A formal [3 + 2] cycloaddition between ynamides and unprotected isoxazol-5-amines has been developed in the presence of catalytic AgNTf2 in an open flask. By the protocol, a variety of functionalized 5-amino-1H-pyrrole-3-carboxamide

• use of an inexpensive catalyst, simple reaction conditions, simple work-up without column chromatographic purification for most of products and high yields. Keywords: [3 + 2] cycloaddition; isoxazole; pyrrole; silver catalysis; ynamide; Introduction Silver-catalyzed transformations of alkynes have

• tethered to cyclohexadienones that can be converted into complex polycycles by Ag-carbenoid-initiated cascades [16]. Recently, Zhu’s group developed a tandem 1,3‑dipolar cycloaddition/cyclopropanation silver-catalyzed reaction of enynals with alkenes [17]. In our previous studies, this silver carbene

Synthetic terpenoids in the world of fragrances: Iso E Super^® is the showcase

• Alexey Stepanyuk and
• Andreas Kirschning

Beilstein J. Org. Chem. 2019, 15, 2590–2602, doi:10.3762/bjoc.15.252

• ) (Scheme 3) [17][18][19][20][21]. To produce Ambrelux (32), myrcene (1) is reacted with dienophile (31) in a Diels–Alder cycloaddition promoted under Lewis-acidic conditions. In order to obtain Iso E Super® (33), Brønstedt acid-mediated cyclisation, similar to the one utilised for the first synthesis of

• described structure [28][32]. Synthetic aspects of individual Iso E Super® components The first target-specific synthesis of (−)-Georgywood® (35) utilised the (S)-Corey–Bakshi–Shibata catalyst (36) for the enantioselective Diels–Alder cycloaddition (Scheme 5). The corresponding enantiomer (+)-Georgywood

• of the oxime derivative of (−)-(1R,2S)-Georgywood® ((−)-35) [33][34]. Corey´s asymmetric synthesis of Iso E Super Plus® ((+)-34) is initiated by a stereoselective Diels–Alder cycloaddition utilizing the CBS catalyst (36) to yield the cyclohexene derivative 42 with good facial selectivity [33

Combining the Ugi-azide multicomponent reaction and rhodium(III)-catalyzed annulation for the synthesis of tetrazole-isoquinolone/pyridone hybrids

• Gerardo M. Ojeda,
• Prabhat Ranjan,
• Pavel Fedoseev,
• Lisandra Amable,
• Upendra K. Sharma,
• Daniel G. Rivera and
• Erik V. Van der Eycken

Beilstein J. Org. Chem. 2019, 15, 2447–2457, doi:10.3762/bjoc.15.237

• prospect of the tetrazole hybridization strategy in drug discovery. Among the most versatile methods for obtaining tetrazoles are the Ugi-azide four-component reaction (Ugi-azide-4CR) [14][15][16] and the 1,3-dipolar cycloaddition of azides with (acyl)cyanides [17][18]. The Ugi-azide-4CR enables the

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• be derived from two acremine F (5) units by a formal [4 + 2] cycloaddition followed by condensation and oxidation. Given the diversity and structural beauty of this class of natural products, it is not surprising that the acremine family has attracted the attention of the synthetic community [6][7][8

• both secondary allylic alcohols and afforded 2 in good overall yield (Scheme 3). Bisacremine E (7) was proposed to be formed in nature via [4 + 2] cycloaddition involving two acremine F (5) units [4]. Although dimerization of 5 through a Diels–Alder cycloaddition is not electronically favorable, we

• starting material. Next, we tried to trigger the cyclization through a [2 + 2] cycloaddition followed by vinyl cyclobutane rearrangement [19][20]. We reasoned that the initially formed divinyl cyclobutane [21] should undergo an allylic rearrangement to furnish the decalin system [22][23]. Condensation

Azologization and repurposing of a hetero-stilbene-based kinase inhibitor: towards the design of photoswitchable sirtuin inhibitors

• Christoph W. Grathwol,
• Nathalie Wössner,
• Sören Swyter,
• Adam C. Smith,
• Enrico Tapavicza,
• Robert K. Hofstetter,
• Anja Bodtke,
• Manfred Jung and
• Andreas Link

Beilstein J. Org. Chem. 2019, 15, 2170–2183, doi:10.3762/bjoc.15.214

• benzoquinoline carboxamide isomers 8a and b formed by photocyclization and successive oxidation (Scheme 3). Furthermore, small amounts of cycloaddition products in two fractions were found, probably due to the high concentration of 2b in the irradiated solution. In contrast, 2f was remarkably stable to long-term

• UV radiation. Even though the ratio of the double bond isomers was left unaffected, only small traces of the cycloaddition product and some unidentified compounds were registered. No formation of benzoquinoline carboxamides was registered as in the case of 2b. Hence, due to the sterically blocking

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• (iodine, bromine) and chalcogens (selenium and tellurium) [18]. While there are several strategies for the synthesis of triazoles, the Cu(II)-catalyzed azide–alkyne cycloaddition reaction (CuAAC click reaction) is considered as one of the most efficient, simple and mild approaches towards the preparation

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• The unusual electronic properties and unique reactivity of fulvenes have interested researchers for over a century. The propensity to form dipolar structures at relatively low temperatures and to participate as various components in cycloaddition reactions, often highly selectively, makes them ideal

• for the synthesis of complex polycyclic carbon scaffolds. As a result, fulvene cycloaddition chemistry has been employed extensively for the synthesis of natural products. More recently, fulvene cycloaddition chemistry has also found application to other areas including materials chemistry and dynamic

• combinatorial chemistry. This highlight article discusses the unusual properties of fulvenes and their varied cycloaddition chemistry, focussing on applications in organic and natural synthesis, dynamic combinatorial chemistry and materials chemistry, including dynamers, hydrogels and charge transfer complexes