Synthesis and characterization of 1,2,3,4-naphthalene and anthracene diimides

• Adam D. Bass,
• Daniela Castellanos,
• Xavier A. Calicdan and
• Dennis D. Cao

Beilstein J. Org. Chem. 2024, 20, 1767–1772, doi:10.3762/bjoc.20.155

• acetylenedicarboxylate (DMAD). Although this [2 + 2 + 2] cycloaddition reactivity strategy has been reported under a variety of aryne generation conditions [17][18][19], in our hands we were only able to generate practical amounts of tetraesters 3 using the method reported by Peña et al. [18]. Hydrolysis of 3 with

Novel route to enhance the thermo-optical performance of bicyclic diene photoswitches for solar thermal batteries

• Akanksha Ashok Sangolkar,
• Rama Krishna Kadiyam and
• Ravinder Pawar

Beilstein J. Org. Chem. 2024, 20, 1053–1068, doi:10.3762/bjoc.20.93

• incorporate all desired features within a single photoswitch is a focus of current research [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The bridged bicyclic diene (BBD)-based NBD/QC couple involves a reversible [2 + 2]-cycloaddition and the chemical transformation during its

(Bio)isosteres of ortho- and meta-substituted benzenes

• H. Erik Diepers and
• Johannes C. L. Walker

Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78

• ) [32]. The synthesis of the corresponding 2-aza-1,5-BCHs 13 was achieved by an intramolecular photochemical [2 + 2] cycloaddition. They were able to employ this synthetic route to synthesise a variety of 1,2-BCPs (±)-14 bearing a protected amine in the bridge position. In early 2023, MacMillan and co

• intramolecular crossed [2 + 2] cycloaddition strategy (Scheme 4C) [36]. They were able to avoid purification by column chromatography by transformation of BCH ester (±)-53 into BCH acid (±)-54, allowing isolation of pure 1,2-BCH (±)-54 by crystallisation. Through their synthesis they were able to access both

• -workers adopted a similar intramolecular [2 + 2] cycloaddition using benzophenone as a triplet sensitizer to access 1,5-BCHs (±)-59a–e as racemic mixtures of endo:exo diastereomers (Scheme 5A) [42]. Basic hydrolysis of the ester moiety followed by recrystallisation gave the diasteromerically pure acid

Enhanced reactivity of Li⁺@C₆₀ toward thermal [2 + 2] cycloaddition by encapsulated Li⁺ Lewis acid

• Hiroshi Ueno,
• Yu Yamazaki,
• Hiroshi Okada,
• Fuminori Misaizu,
• Ken Kokubo and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2024, 20, 653–660, doi:10.3762/bjoc.20.58

• derivatization of this novel material. In this study, we report the synthesis of Li+@C60 derivatives via the thermal [2 + 2] cycloaddition reaction of styrene derivatives, achieving significantly higher yields of monofunctionalized Li+@C60 compared to previously reported reactions. Furthermore, by combining

• experimental and theoretical approaches, we clarified the range of applicable substrates for the thermal [2 + 2] cycloaddition of Li+@C60, highlighting the expanded scope of this straightforward and selective functionalization method. Keywords: electron transfer; fullerene; ion-endohedral fullerene; Lewis

• acid catalyst; thermal [2 + 2] cycloaddition; Introduction Chemical functionalization of fullerenes is a fascinating and extensively studied approach, playing a pivotal role in fullerene-based materials science to introduce various characteristic functionalities [1][2][3][4][5][6][7]. Significant

Unveiling the regioselectivity of rhodium(I)-catalyzed [2 + 2 + 2] cycloaddition reactions for open-cage C₇₀ production

• Cristina Castanyer,
• Anna Pla-Quintana,
• Anna Roglans,
• Albert Artigas and
• Miquel Solà

Beilstein J. Org. Chem. 2024, 20, 272–279, doi:10.3762/bjoc.20.28

• holds significant promise for applications in the fields of medicinal chemistry, materials science, and photovoltaics. In this study, we investigate the regioselectivity of the rhodium(I)-catalyzed [2 + 2 + 2] cycloaddition reactions between diynes and C70 as a novel procedure for generating C70 bis

• to be able to produce meaningful changes in the reactivity of the cage [28][29][30][31][32]. In 2018, our group reported a catalytic process to transform C60 in bis(fulleroid) derivatives [33][34][35]. This transformation encompassed a partially intermolecular Rh-catalyzed [2 + 2 + 2] cycloaddition

• unexpectedly, the [6,6]-bond in C60 was the one involved in this [2 + 2 + 2] cycloaddition. Although there are several papers reporting the opening of a hole in C70 [39][40][41][42][43][44][45], this chemistry has been less explored than in C60. The lower D5h symmetry of C70 compared to the Ih of C60 increases

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• Michio Yamada Department of Chemistry, Tokyo Gakugei University, Nukuikitamachi 4-1-1, Koganei, Tokyo 184-8501, Japan 10.3762/bjoc.20.13 Abstract Various push–pull chromophores can be synthesized in a single and atom-economical step through [2 + 2] cycloaddition–retroelectrocyclization (CA–RE

• of click-type [2 + 2] cycloaddition (CA)–retroelectrocyclization (RE) reactions, offering means for preparing these coveted push–pull chromophores [7]. A review conducted in 2023 comprehensively explored the optoelectronic properties of TCBDs along with their photovoltaic applications [8]. The

• reactions. In these reactions, the nucleophilic attack of the alkyne carbon of 1 occurs at the C(1) carbon of 6. When the formal [2 + 2] cycloaddition, as delineated in path A, occurs for the zwitterionic intermediate featuring the 1,1,3-tricyanoallyl anion obtained through the nucleophilic attack

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations

• Laura Abella,
• Gerard Novell-Leruth,
• Josep M. Ricart,
• Josep M. Poblet and
• Antonio Rodríguez-Fortea

Beilstein J. Org. Chem. 2024, 20, 92–100, doi:10.3762/bjoc.20.10

• the reaction either via singlet excitation or via radical cation formation (Scheme 1). Estimation of the activation barrier for the [2 + 2] cycloaddition when the nanotube acts as a sensitizer is 33.5 ± 6.8 kJ mol−1. This value agrees with computational predictions for the reaction via an excited

• analyzed the interaction between C60 and the nanotube within the peapod. Next, we have found that some dimeric C60–C60 fullerene structures inside the carbon nanotube are thermodynamically favorable. Experiments indicate that, besides C60 sensitization via a singlet excited state, the [2 + 2] cycloaddition

• + 2] cycloaddition in phase 1 We analyzed in detail the energy profile for the first step in the dimerization process, that is, the reversible [2 + 2] cycloaddition to obtain dimers 1-Cs and 1-D2h. We initially considered dimerization in the gas phase to check the reliability of our methodology

Biphenylene-containing polycyclic conjugated compounds

• Cagatay Dengiz

Beilstein J. Org. Chem. 2023, 19, 1895–1911, doi:10.3762/bjoc.19.141

• ] cycloaddition [19][20], [2 + 2 + 2] cycloaddition [21], and the Ullmann reaction [15][22] (Scheme 1). Due to the observed low yields in flash vacuum pyrolysis, the difficulty in synthesizing starting materials, such as 3, and the impractical nature of scaling up the method for large quantities, the other three

• -catalyzed formal [2 + 2] cycloaddition reactions but also the emergence of tetracene trimer 86 and tetramer 88 stemming from [2 + 2 + 2] cycloaddition reactions (Scheme 18). It is proposed that an aryne intermediate is formed after thermal activation and that the observed end products are formed from arynes

• resulting from a [2 + 2] cycloaddition and trimer 90 formed via a [2 + 2 + 2] cycloaddition pathway were observed. In contrast, when applied to Au(100), only the dimer structure 91 was generated through the [2 + 2] cycloaddition process. In a recent study in this field, Izydorczyk et al. were able to

The unique reactivity of 5,6-unsubstituted 1,4-dihydropyridine in the Huisgen 1,4-diploar cycloaddition and formal [2 + 2] cycloaddition

• Xiu-Yu Chen,
• Hui Zheng,
• Ying Han,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2023, 19, 982–990, doi:10.3762/bjoc.19.73

• -dihydropyridines in acetonitrile at room temperature afforded functionalized isoquinolino[1,2-f][1,6]naphthyridines in good yields and with high diastereoselectivity. More importantly, the formal [2 + 2] cycloaddition reaction of dialkyl acetylenedicarboxylates and 5,6-unsubstituted 1,4-dihydropyridines in

• refluxing acetonitrile gave unique 2-azabicyclo[4.2.0]octa-3,7-dienes as major products and 1,3a,4,6a-tetrahydrocyclopenta[b]pyrroles as minor products via further rearrangement. Keywords: 1,4-dihydropyridine; electron-withdrawing alkyne; formal [2 + 2] cycloaddition; Huisgen's 1,4-dipole; isoquinoline

• acetylenedicarboxylate and 5,6-unsubstituted 1,4-dihydropyridines with N–Ar groups did not give the above isoquinolino[1,2-f][1,6]naphthyridines, but the unique 2-azabicyclo[4.2.0]octa-3,7-diene-7,8-dicarboxylates were isolated in moderate yields. These products were obviously produced from the formal [2 + 2

Strategies in the synthesis of dibenzo[b,f]heteropines

• David I. H. Maier,
• Barend C. B. Bezuidenhoudt and
• Charlene Marais

Beilstein J. Org. Chem. 2023, 19, 700–718, doi:10.3762/bjoc.19.51

• ) chloride (Scheme 26). Alkyne–carbonyl metathesis is proposed to proceed via [2 + 2] cycloaddition and –reversion steps, catalysed by a Brønsted or Lewis acid, with the catalyst proposed to form a σ-complex with the carbonyl group and/or a π-complex with the alkyne [68]. 3.7 Hydroarylation The construction

Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

Germacrene B – a central intermediate in sesquiterpene biosynthesis

• Houchao Xu and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2023, 19, 186–203, doi:10.3762/bjoc.19.18

• acetone and water to a hemiacetal that can decompose to 11 (Scheme 4B) [43]. Furthermore, 1 shows an interesting photochemistry (Scheme 4C). A [2 + 2] cycloaddition of the endocyclic double bonds yields 12 whose formation is understandable from conformers 1c and 1d. The all-cis stereoisomer 14 requires a

• photochemical E/Z isomerisation to 13 prior to [2 + 2] cycloaddition. Further photochemical products from 1 include 5, 15 that may be formed through a biradical mechanism, and rearranged 16 [51]. Germacrene B (1) has planar chirality (Scheme 4D), but recovery of the starting material from an incomplete

Preparation of an advanced intermediate for the synthesis of leustroducsins and phoslactomycins by heterocycloaddition

• Anaïs Rousseau,
• Guillaume Vincent and
• Cyrille Kouklovsky

Beilstein J. Org. Chem. 2022, 18, 1385–1395, doi:10.3762/bjoc.18.143

• alcohol. Studies in fragment coupling We have previously reported the synthesis of the lactone fragment by catalytic asymmetric [2 + 2] cycloaddition followed by ring extension [18]. The initial product was the TMS-acetylene 18 which could be easily desilylated to give 21. However, model studies for

Unusual highly diastereoselective Rh(II)-catalyzed dimerization of 3-diazo-2-arylidenesuccinimides provides access to a new dibenzazulene scaffold

• Anastasia Vepreva,
• Alexander S. Bunev,
• Andrey Yu. Kudinov,
• Grigory Kantin,
• Mikhail Krasavin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2022, 18, 533–538, doi:10.3762/bjoc.18.55

• ortho-methyl substituent in the benzylidene fragment. In this case, along with conventional reaction products ‒ dimer 2r and indene 3r, unexpectedly the cyclobutane 5, a product of the formal [2 + 2] cycloaddition, was isolated in low yield (Scheme 1); its structure was confirmed by single-crystal X-ray

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• -LED light [111]. Under these conditions, menadione (10) and terminal alkynes 66 underwent a [2 + 2] cycloaddition reaction generating compounds containing cyclobutene rings (67a–c), that are important precursors in natural products syntheses. It is important to note that the choice of the blue-LED

Borylated norbornadiene derivatives: Synthesis and application in Pd-catalyzed Suzuki–Miyaura coupling reactions

• Robin Schulte and
• Heiko Ihmels

Beilstein J. Org. Chem. 2022, 18, 368–373, doi:10.3762/bjoc.18.41

• recently gained considerable attention because of its ability to store light-energy by the photo-induced intramolecular [2 + 2] cycloaddition to the metastable quadricyclane [1][2][3][4][5][6][7]. The latter may be transformed back to the starting norbornadiene in an exothermic process upon heating or

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• ], rhodium-mediated alkyne [2 + 2 + 2] cycloaddition reactions [3], and the palladium-catalysed aerobic domino Suzuki coupling/Michael addition reaction [4]. The most attractive and common strategies to phenanthridines rely on intramolecular cyclizations of various ortho-functionalized biaryl precursors

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• -cyclotrimerization reaction catalyzed by a cobalt/zinc reagent [40]. With regard to substituted anthracenes, this method consisted of a [2 + 2 + 2] cycloaddition reaction of 1,6-diynes 27 with 4-aryl-2-butyn-1-ols 28 (Scheme 6). The authors converted the resulting benzylic alcohols 29 to the corresponding aldehydes

• + 2 + 2] cycloaddition of 1,2-bis(propiolyl)benzene derivative 178 and terminal/internal alkynes 177 (Scheme 41) [75]. The authors performed the reactions with terminal alkynes in toluene, and reactions with internal alkynes in dichloromethane (DCM). They noted that the use of 1,2-bis

• -Proline-catalyzed [4 + 2] cycloaddition reaction of naphthoquinones and α,β-unsaturated aldehydes. Iridium-catalyzed [2 + 2 + 2] cycloaddition of a 1,2-bis(propiolyl)benzene derivative with alkynes. Synthesis of several anthraquinone derivatives by using InCl3 and molecular iodine. Indium-catalyzed

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• based on DFT calculations. A different [2 + 2]-cycloaddition process was suggested to rationalize the observed OH-selectivity. In 2015, Padrón and co-workers also reported the Prins cyclization catalyzed by a Fe(III) and trimethylsilyl halide system for the synthesis of all-cis-2,4,6-trisubstituted THP

• [107]. As reported previously by Feng et al. [106], two mechanistic pathways via the classical oxocarbenium route and [2 + 2]-cycloaddition were considered for DFT calculations. Experimental and DFT studies suggested the preference of a classical oxocarbenium route over the [2 + 2]-pathway for those

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• produced (−)-inthomycin C ((−)-3) in 80% yield with high enantiopurity (Scheme 7). In 2012, Hatakeyama and co-workers reported a unified strategy for the asymmetric total syntheses of inthomycin A ((+)-1), inthomycin B ((+)-2), and inthomycin C ((−)-3), starting with an organocatalytic asymmetric [2 + 2

• ] cycloaddition reaction of an aldehyde and a ketene followed by their isomerization-free Stille coupling with (E)-5-(3-(tributylstannyl)allyl)oxazole (Schemes 8–10) [22]. In this synthesis, the enantiopure β-lactone (+)-79a was synthezised from (Z)-aldehyde 78 and propionyl chloride according to Nelson’s method

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• -deficient alkenes 190 to synthesise cyclobutanes 191 (Scheme 28c) [83]. Recently, Bach et al. also employed this methodology for the intramolecular [2 + 2] cycloaddition of quinolones 192 containing either a pendant alkene or allene to obtain cyclobutanes 193 (Scheme 28d) [84]. Recently, ent-185 was applied

• and enantioselectivities (27 examples, up to >99:1 er). Yoon et al. have also shown that these types of Lewis acid complexes can be used in an energy transfer process for the [2 + 2] cycloaddition of enones 288 with alkenes 289 (Scheme 47) [113][114]. The triplet energy of 288, when complexed to the

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• consider the reactivity of the electrophilic (“electron-poor”) acetylenic bond toward 1,3-dienes, and show how the expected [4 + 2] or [2 + 2] cycloaddition products can enter subsequent cascade reactions toward carbocycles which incorporate a C(CF3)NMe2 structural unit. Results and Discussion The Diels

• -Cb for the byproduct. Thus, signals of the two methyl groups (δ 1.63, 1.78 ppm) and two terminal olefinic protons (δ 4.88 ppm, m) are observed, and the ring-CH2 protons appear as an AB spin system (δ 2.75 and 2.92 ppm, 2J = 15.2 Hz). Obviously, 4-Cb and 5-Cb result from a formal [2 + 2] cycloaddition

• presumably renders an ionic [2 + 2] cycloaddition pathway competitive with the Diels–Alder reaction. The few reported examples of cyclobutene formation from alkynes and unactivated 1,3-dienes include the sensitized photocycloaddition of phenylacetylene and DMBD [30] and the gold(I)-catalyzed reaction of

NHC-catalyzed enantioselective synthesis of β-trifluoromethyl-β-hydroxyamides

• Alyn T. Davies,
• Mark D. Greenhalgh,
• Alexandra M. Z. Slawin and
• Andrew D. Smith

Beilstein J. Org. Chem. 2020, 16, 1572–1578, doi:10.3762/bjoc.16.129

• Alyn T. Davies Mark D. Greenhalgh Alexandra M. Z. Slawin Andrew D. Smith EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United Kingdom 10.3762/bjoc.16.129 Abstract The N-heterocyclic carbene (NHC)-catalyzed formal [2 + 2] cycloaddition between α

• moderate to good yield as a single diastereoisomer. Keywords: enantioselective catalysis; formal [2 + 2] cycloaddition; N-heterocyclic carbene; ring opening; trifluoromethyl group; Introduction The trifluoromethyl unit holds a prominent and privileged position within organic chemistry [1][2][3][4][5][6

• paper, this formal [2 + 2] protocol is extended to the use of trifluoroacetophenones to develop an enantioselective route to β-trifluoromethyl-β-hydroxy carboxylic acid derivatives (Figure 2C). Results and Discussion Optimization Optimization of the NHC-catalyzed formal [2 + 2] cycloaddition using the α

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• as the HAT cocatalyst, to generate the tetralin skeleton, which is widely seen in drugs and pesticide synthesis (Scheme 5) [13]. Diphenyl disulfide played an important role in the [4 + 2] cycloaddition process. Without diphenyl disulfide, only the product of the [2 + 2] cycloaddition was observed

• nonpolar solvent, PhSSPh accelerates the [4 + 2] cycloaddition of the radical cation 19, but the electron-relay catalyst promotes the [2 + 2] cycloaddition. The radical cation 19 can undergo two different types of cyclizations, subject to the relative reactivity of its radical and cation center. The α