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

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

• 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

• rearrangement (Scheme 39) [89]. Further photochemical [2 + 2] cycloaddition and hydrolysis allowed them to obtain rhodonoid A in 30% overall yield. Other similar natural products (rhodonoid B, E and F) were also prepared by the same synthetic strategy. Singlet oxygen has also been efficiently used for

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

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

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

• 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

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

• derivative [22][27]. Reaction scheme for (a) [2 + 2] cycloaddition of 1,2-diphenylmethylenecyclopropene and 1-diethylamino-1,3-butadiene and (b) [4 + 2] cycloaddition of an in situ-generated triafulvene with cyclopentadiene. Diels–Alder cycloaddition of pentafulvenes derivatives participating as dienes with

Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS)

• Philipp P. Könen and
• Matthias Wüst

Beilstein J. Org. Chem. 2019, 15, 1945–1961, doi:10.3762/bjoc.15.190

• photoinduced [2 + 2]-cycloaddition is very unlikely. The biosynthesis of β-bourbonene can be performed by cationic cyclization, as shown in Scheme 4. A total of 5 bicyclic, aromatic sesquiterpene hydrocarbons (21–25) with a cadinane skeleton were found in exocarp of the grape variety Lemberger, whose identity

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• (NBD) and quadricyclanes (QC) attached to TATA and TOTA platforms which can be used to check if these accelerated rates and the spin change mechanism also apply to [2 + 2] cycloreversions (QC→NBD). Keywords: [2 + 2] cycloaddition; [2 + 2] cycloreversion; norbornadiene; photochemical isomerization

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• , inexpensive, water-tolerant Lewis acid catalyst in the formation of both carbon–carbon and carbon–heteroatom bonds, and thereby the formation of various biologically promising organic compounds [68]. Important advances in scandium-catalyzed chemistry include [4 + 2] and [2 + 2] cycloaddition reactions, Baeyer

SO₂F₂-mediated transformation of 2'-hydroxyacetophenones to benzo-oxetes

• Revathi Lekkala,
• Ravindar Lekkala,
• Balakrishna Moku,
• K. P. Rakesh and
• Hua-Li Qin

Beilstein J. Org. Chem. 2019, 15, 976–980, doi:10.3762/bjoc.15.95

• + 2] cycloaddition that furnishes substituted oxetanes rapidly, for example Paterno–Büchi reaction (Scheme 1b) [21]. However, the recognition of facial selectivity control in [2 + 2] cycloaddition is not an easy task. The availability of various methods for the synthesis of oxetanes and their strained

• intramolecular etherification reaction, which is called Williamson ether synthesis (Scheme 1a). This method was first utilized to synthesize oxetanes in 1878 and has remained as general tool in the synthesis of complex oxetane-containing compounds since then [17][18][19][20]. The second strategy involves a [2

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• (Figure 21a). However, 1,8-dipyridylnaphthalene was used as hydrogen-bond acceptor for the [2 + 2] cycloaddition of fumaric acid derivatives (Figure 21b). In 2017 Purse and co-workers reported the host–guest chemistry of pyrogallo[4]arene (39) hexamers under mechano-milling conditions [94]. A hexameric

• , supramolecular catalysis proposes a much simpler model to understand the catalytic activity of enzymes. In 2010, MacGillivray and co-workers have demonstrated the concept of “supramolecular catalysis” in a hydrogen-bond-assisted self-assembled formation of a [2 + 2]-cycloaddition product. The reaction was found

• thermodynamic control. Preferential formation of hexamer 33 under mechanochemical shaking via non-covalent interactions of peptide chains. Anion templated mechanochemical synthesis of macrocycles cycHC[n] by validating the concept of dynamic covalent chemistry. Hydrogen-bond-assisted [2 + 2]-cycloaddition

Aqueous olefin metathesis: recent developments and applications

• Valerio Sabatino and
• Thomas R. Ward

Beilstein J. Org. Chem. 2019, 15, 445–468, doi:10.3762/bjoc.15.39

• intermediate (Scheme 2, intermediates II and IV) [16]. The catalytic cycle involves an initial [2 + 2] cycloaddition between a metal carbene I and an olefin, followed by a retro [2 + 2] cycloaddition, leading to the release of a “scrambled” olefin (e.g., ethylene in Scheme 2) and the metal carbene species III

• as key intermediate. A [2 + 2] cycloaddition with a second olefin leads to the formation of intermediate IV, followed by a retro [2 + 2] cycloaddition that regenerates catalyst I and releases the metathesis product. This visionary mechanistic proposal was later confirmed by experimental studies [17

Dispersion-mediated steering of organic adsorbates on a precovered silicon surface

• Lisa Pecher,
• Sebastian Schmidt and
• Ralf Tonner

Beilstein J. Org. Chem. 2018, 14, 2715–2721, doi:10.3762/bjoc.14.249

• . The adsorption of a first molecule of 1 on Si(001) is characterized by a direct adsorption path without intermediate structure leading to a strongly covalently bonded [2 + 2] cycloaddition product 2 as summarized in Scheme 1 with ring strain being decisive for the high reactivity of 1 [5][6][8]. Not

• minimization without symmetry constraints leads to a structure with a local C2 rotational axis resulting in symmetry-equivalent molecules 1 and 1′. Energies and Gibbs energies of adsorption were previously found to support the notion of strong covalent bonding for the [2 + 2] cycloaddition of 1 on the silicon

• found for the adsorption of molecules on precovered surfaces [24]. The bonding in the covalent [2 + 2] cycloaddition product (i.e., the final state of adsorption) is thus very similar for clean and precovered surfaces. But the reaction path leading to this state might still be qualitatively changed by

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• [2 + 2 + 2] cycloaddition of diynes and CO2 proceeds to afford pyrones. Keywords: carbon dioxide; carboxylation; cobalt; homogeneous catalysts; rhodium; Introduction Carbon dioxide (CO2) is one of the most important materials as renewable feedstock [1][2][3][4]. However, the thermodynamic and

• (Scheme 38). [2 + 2 + 2] Cycloaddition of diynes with CO2 The [2 + 2 + 2] cycloaddition of diynes with CO2 is an important reaction in the field of CO2 fixation. In these reactions, cyclic esters such as pyrones can be obtained, which are classically catalyzed by Ni complexes [76][77][78]. Tanaka et al

• . reported that a Rh complex with a suitable bidentate ligand was an efficient catalyst for the [2 + 2 + 2] cycloaddition reaction (Scheme 39) [79]. The reaction of 43a was performed using 20 mol % [Rh(cod)2]BF4 and a bidentate phosphine in 1,2-dichloroethane at room temperature. Prior to the addition of 43a

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• structure of 86 was confirmed by the spectroscopic data. The formation of the heptafulvalenes could be explained via an intermolecular [2 + 2] cycloaddition product such as 87 between the carbonyl group of tropones and the ketene C=C double bond of 8-oxoheptafulvene (85) followed by decarboxylation. In a

Addition of dithi(ol)anylium tetrafluoroborates to α,β-unsaturated ketones

• Yu-Chieh Huang,
• An Nguyen,
• Simone Gräßle,
• Sylvia Vanderheiden,
• Nicole Jung and
• Stefan Bräse

Beilstein J. Org. Chem. 2018, 14, 515–522, doi:10.3762/bjoc.14.37

• -dithioacetals [4] are of particular interest as attractive nucleophiles for the addition to halonium ions [5][6], acyl chlorides [7] and other electrophiles [8][9][10] and are broadly used as precursors for [2 + 2]-cycloaddition [11][12], (aza)-Diels–Alder reaction [13][14], and [3 + 2]-cycloaddition reactions

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

• includes the reduction to form alkane 8 [3], oxidative cleavage of the C=C bond to form 9 [4], ring-opening metathesis to form functionalized alkenes 10 and 11 [4], dihydroxylation to form diol 12 [5], ruthenium-catalyzed [2 + 2] cycloaddition with unsymmetrical alkynes to form regioisomers 13 and 14 [6

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

• thiophene derived sulfur ylide 12. Cyclopropanation of dimethyl dicyanofumarate (E-1b) through a stepwise reaction with the in situ generated thiocarbonyl S-isopropanide 16a. The [2 + 2]-cycloadditions of dimethyl dicyanofumarate (E-1b) with electron-rich ethylenes 20 and 22. The [2 + 2]-cycloaddition of

• isomeric dimethyl dicyanofumarate (E-1b) and dicyanomaleate (Z-1b) with N-vinylcarbazole (25). Non-concerted [2 + 2]-cycloaddition between E-1b and bicyclo[2.1.0]pentene (27). Stepwise [3 + 2]-cycloadditions of some thiocarbonyl S-methanides with dialkyl dicyanofumarates E-1 and dicyanomaleates Z-1

Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• ., cyclopentenone 239) with alkynes in the presence of nickel and aluminum complexes [108]. This [2 + 2 + 2] cycloaddition run with a high regioselectivity and led mostly to meta isomers. The authors used, as catalytic systems, the following complexes: Ni(acac)2, Ni(cod)2, Me3Al, Me2Al(OPh), MeAl(OPh)2 and Al(OPh)3

• et al. have further expanded the scope of this reaction on several other substrates which are active in the [2 + 2 + 2] cycloaddition [120]. For example, the triyn 322 under hexadehydro-Diels–Alder (HDDA) conditions gave the corresponding 1-indanone 323 in 80% yield (Scheme 89). 3.2 From furans Van

Stereodynamic tetrahydrobiisoindole “NU-BIPHEP(O)”s: functionalization, rotational barriers and non-covalent interactions

• Golo Storch,
• Sebastian Pallmann,
• Frank Rominger and
• Oliver Trapp

Beilstein J. Org. Chem. 2016, 12, 1453–1458, doi:10.3762/bjoc.12.141

• phases [22]. However, introduction of functional groups which enable a modular derivatization approach is often hampered by long and tedious synthetic procedures. Doherty et al. reported a rhodium catalyzed double [2 + 2 + 2] cycloaddition strategy for a convergent synthesis of “NU-BIPHEP”s [23]. In this

• well as rotational barriers are studied in solution by (D)HPLC techniques. Results and Discussion Synthesis of tetrahydrobiisoindole “NU-BIPHEP(O)s” The rhodium catalyzed double [2 + 2 + 2] cycloaddition of 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne and a variable diyne compound is the key step in the

• + 2 + 2] cycloaddition. B) Acidic deprotection of tetrahydrobiisoindole “NU-BIPHEP(O)” 1c and subsequent amide bond formation with 3,5-dichlorobenzoyl chloride. Investigation of 3,5-dichlorobenzoyl modified tetrahydrobiisoindole “NU-BIPHEP(O)” 3. A) Three signal sets are observed in 31P{1H} NMR

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• two important factors to consider when putting together such a mechanism: coordination of the propargyl alcohol on the metal center and facial selectivity for the [2 + 2] cycloaddition. We will look at each in turn. First, coordination by the propargyl alcohol creates four possible diastereomeric

• for either coordination mode, which leads to poorer enantioselectivities in THF (Table 8, entry 6). We propose that acetone, being more Lewis basic than THF, has the effect of epimerizing the chiral-at-ruthenium intermediates formed prior to [2 + 2] cycloaddition. The rate of epimerization is much

• faster than the [2 + 2] cycloaddition, creating a classic Curtin–Hammitt scenario wherein all of the substrate is funneled into the observed enantiomer of product (Scheme 8). Rate k1 is much slower than k2 due to the severe steric hindrance imposed by the ligated chiral sulfoxide, which block alkene

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• this reaction is that it can be transferred to large-scale chemical production, due to the difference in the solubilities of the reactants and the products, which means the product and the catalyst can be isolated separately. In 2012, Carrillo and co-workers reported an enantioselective formal [2 + 2

• ] cycloaddition of enals 237 with nitroalkenes 238 to obtain the oxabicyclo product 239 (Scheme 74) [93]. A combination of catalysts was used, with catalysts 23 and 214. This reaction affords the desired product in 38–91% yield and 85–95% ee. Furthermore, a thiourea catalyzed reaction via a cationic

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

• Laura A. Bryant,
• Rossana Fanelli and
• Alexander J. A. Cobb

Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46

• -amination using β-ICPD. Meng’s cupreidine catalyzed α-hydroxylation. Shi’s biomimetic transamination process for the synthesis of α-amino acids. β-Isocupreidine catalyzed [4 + 2] cycloadditions. β-Isocupreidine catalyzed [2+2] cycloaddition. A domino reaction catalyst by cupreidine catalyst CPD-30. (a

Natural products from microbes associated with insects

• Christine Beemelmanns,
• Huijuan Guo,
• Maja Rischer and
• Michael Poulsen

Beilstein J. Org. Chem. 2016, 12, 314–327, doi:10.3762/bjoc.12.34

• extract led to the isolation of a new tricyclic macrolactam named tripartilactam (24) [103]. Tripartilactam (24) contains an unprecedented cyclobutane moiety, which links the 8- and 18-membered rings, and it is most likely derived from a photochemically [2 + 2] cycloaddition reaction of the corresponding