HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

• Luan A. Martinho and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2024, 20, 628–637, doi:10.3762/bjoc.20.55

• single report on the use of a heteropolyacid (phosphomolybdic acid) in the GBB reaction but for a limited number of examples (Scheme 1a) [50]. That caught our attention for being the only example so far of a room temperature GBB reaction carried out in less than an 18-hour period. However, at least in

A myo-inositol dehydrogenase involved in aminocyclitol biosynthesis of hygromycin A

• Michael O. Akintubosun and
• Melanie A. Higgins

Beilstein J. Org. Chem. 2024, 20, 589–596, doi:10.3762/bjoc.20.51

• , the pellet was resuspended in 40 mL of sucrose solution (25% sucrose, 50 mM Tris pH 8) using continuous stirring. Then, 10 mg of lysozyme (Bio Basic) was added and stirred at room temperature for 10 min, followed by the addition of 80 mL deoxycholate solution (1% deoxycholate, 1% Triton X-100, 100 mM

Entry to new spiroheterocycles via tandem Rh(II)-catalyzed O–H insertion/base-promoted cyclization involving diazoarylidene succinimides

• Alexander Yanovich,
• Anastasia Vepreva,
• Ksenia Malkova,
• Grigory Kantin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2024, 20, 561–569, doi:10.3762/bjoc.20.48

• the reaction in the presence of DIPEA proceeded selectively, albeit more slowly. By increasing the DIPEA loading to 50 mol %, the product 2a was isolated in 75% yield after incubation for 7 days at room temperature. The structure of the obtained spirobutenolide was confirmed by single crystal X-ray

• data. Further syntheses of spirobutenolides 2 were performed under the one-pot conditions: after completion of the first O–H insertion step, a base was added to the reaction mixture and kept at room temperature until completion of the cyclization step, controlled by TLC. The results of the syntheses

• cyclization step was more selective and the total yield of the desired product was higher. The 6-exo-tet cyclization of intermediate compounds 16 under the action of DBU in acetone at room temperature proceeded within a few minutes, which is much faster than in the case of compounds 14. This can be explained

Synthesis and biological profile of 2,3-dihydro[1,3]thiazolo[4,5-b]pyridines, a novel class of acyl-ACP thioesterase inhibitors

• Jens Frackenpohl,
• David M. Barber,
• Guido Bojack,
• Birgit Bollenbach-Wahl,
• Ralf Braun,
• Rahel Getachew,
• Sabine Hohmann,
• Kwang-Yoon Ko,
• Karoline Kurowski,
• Bernd Laber,
• Rebecca L. Mattison,
• Thomas Müller,
• Anna M. Reingruber,
• Dirk Schmutzler and
• Andrea Svejda

Beilstein J. Org. Chem. 2024, 20, 540–551, doi:10.3762/bjoc.20.46

• ). Whilst tetrabutylammonium borohydride [22] at room temperature did not lead to a conversion of the starting material 5 either, a trace amount of desired 2,3-dihydro[1,3]thiazolo[4,5-b]pyridine 7b was formed at elevated temperature, accompanied by disulfide 18b as the main product (Table 1, entries 5 and

• (13b): To a stirred mixture of 6-bromopyridin-2-amine (8, 10.00 g, 56.88 mmol, 1.00 equiv), 2-fluorophenylboronic acid (9.52 g, 65.98 mmol, 1.16 equiv), and Na2CO3 (12.06 g, 113.8 mmol, 2.00 equiv) in a mixture of 1,4-dioxane (80 mL) and water (80 mL) at room temperature was added Pd(dppf)Cl2 (1.67 g

• , 2.28 mmol, 0.04 equiv), and the mixture was stirred at 80 °C for 3 h. Thereafter, the reaction mixture was cooled to room temperature, diluted with water, and extracted thoroughly with ethyl acetate. The combined organic layer was washed with brine, dried over Na2SO4, filtered, and concentrated under

Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

• coordination-switchable tweezers for switching between two magnetic states that are stable at room temperature [44]. To increase the magnetic coupling between the metal center the group investigated the Mn(III)–salphen tweezers 14 that can coordinate in apical position to cyanide ions. The complexation of CN

• electrostatic repulsion between the doubly charged redox-active units. Thus, it can be concluded that, although the tweezers exhibit different conformations in neutral and oxidized states, at room temperature

A new analog of dihydroxybenzoic acid from Saccharopolyspora sp. KR21-0001

• Rattiya Janthanom,
• Yuta Kikuchi,
• Hiroki Kanto,
• Tomoyasu Hirose,
• Arisu Tahara,
• Takahiro Ishii,
• Arinthip Thamchaipenet and
• Yuki Inahashi

Beilstein J. Org. Chem. 2024, 20, 497–503, doi:10.3762/bjoc.20.44

• wavelengths of 200 to 800 nm. Optical rotation was measured using a P-2200 polarimeter (JASCO). De-sulfurization and hydrolyzation KR21-0001A (1) (1 mg) was dissolved in EtOH (0.5 mL) and treated with skeletal Ni (1 mg). The reaction mixture was stirred for 13 h at room temperature under H2 (Figure S6

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• % conversion after 24 h, estimated t1/2 = 96 h, kobs = 1.4 × 10−6 s−1). With 55 μL MeOH in DCM, the relative rates for each substrate are 3,850:50:1 with urea 1a > carbamate 1b > benzamide 1c. The analogous toluene sulfonamide substrate 1d did not react on measurable timescales at room temperature (no product

• have been masked by the high temperatures and long reaction times of early reports. For example, Widenhoefer engaged carbamates and amides in dioxane at temperatures >80 °C [12][13]. Later work showed that ureas could be engaged at room temperature when a NHC–gold catalyst system was used, outpacing

Pseudallenes A and B, new sulfur-containing ovalicin sesquiterpenoid derivatives with antimicrobial activity from the deep-sea cold seep sediment-derived fungus Pseudallescheria boydii CS-793

• Zhen Ying,
• Xiao-Ming Li,
• Sui-Qun Yang,
• Hong-Lei Li,
• Xin Li,
• Bin-Gui Wang and
• Ling-Hong Meng

Beilstein J. Org. Chem. 2024, 20, 470–478, doi:10.3762/bjoc.20.42

• medium at 28 °C for five days, which were then inoculated into the noted rice solid medium in 1 L Erlenmeyer flasks and static cultivation for 30 days at room temperature. After fermentation, it was fragmented mechanically and extracted thoroughly with EtOAc. The combined extracts were filtered and

(E,Z)-1,1,1,4,4,4-Hexafluorobut-2-enes: hydrofluoroolefins halogenation/dehydrohalogenation cascade to reach new fluorinated allene

• Nataliia V. Kirij,
• Andrey A. Filatov,
• Yurii L. Yagupolskii,
• Sheng Peng and
• Lee Sprague

Beilstein J. Org. Chem. 2024, 20, 452–459, doi:10.3762/bjoc.20.40

• was complex, we focused our attention on carrying out the reaction with KOH. The best result was obtained by treatment of 1 equivalent of butane 2 with 1.3 equivalents of KOH in the presence of 5 mol % of Bu4NBr as an interfacial carrier in water at room temperature for 2 h (Table 1, entry 7). After

• room temperature MgBrF was produced together with allene 11 (Scheme 8). In addition to the allene, the formation of olefin 1b was also recorded in the 19F NMR spectrum. Unfortunately, due to difficulties in separating from olefin 1b and diethyl ether, allene 11 was not isolated in a pure state

• increase the lithiation reaction time. Based on the results obtained, it was logical to assume that the reaction can be carried out with a mixture of 3a,b. We found that the reaction of 3a,b with 1.2 equivalents of BuLi in heptane at −80 °C for 1 hour, followed by warming to room temperature, led to the

Enhanced host–guest interaction between [10]cycloparaphenylene ([10]CPP) and [5]CPP by cationic charges

• Eiichi Kayahara,
• Yoshiyuki Mizuhata and
• Shigeru Yamago

Beilstein J. Org. Chem. 2024, 20, 436–444, doi:10.3762/bjoc.20.38

• that the complex formation occurs between neutral [10]CPP and [5]CPP2+ forming [10]CPP⊃[5]CPP2+ (Figure 1c, path A) [21]. The absence of signals in the ESR measurements at room temperature also suggests the formation of complexes with a closed-shell electronic structure. The same complex was formed

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

• the synthesis of BIMs, using a catalytic amount of I2 under solvent-free conditions at room temperature (Scheme 8) [91]. The differentiating factor of this technique is the employment of solid grind, which avoids the need for a reaction medium, while also utilizing the same amount of I2 (20 mol

• -free and room temperature conditions. In these optimized conditions, several aromatic aldehydes and indoles formed the respective BIMs in excellent yields (84–95%), without any noteworthy differences between the various carbonyl substrates. Indoles, substituted at the 2’ position, were much more

Facile approach to N,O,S-heteropentacycles via condensation of sterically crowded 3H-phenoxazin-3-one with ortho-substituted anilines

• Eugeny Ivakhnenko,
• Vasily Malay,
• Pavel Knyazev,
• Nikita Merezhko,
• Nadezhda Makarova,
• Oleg Demidov,
• Gennady Borodkin,
• Andrey Starikov and
• Vladimir Minkin

Beilstein J. Org. Chem. 2024, 20, 336–345, doi:10.3762/bjoc.20.34

• -phenoxazin-3-ones 4, compounds 5 and 6 display intense fluorescence in solution at room temperature (Figure 5). The excitation spectra of the compounds (Figures S7–S11, Supporting Information File 1) correspond to the longest-wavelength absorption bands. The absorption and emission spectra of benzo[5,6][1,4

• 6a,b) and c = 2⋅10−6 M (compound 10c) in toluene solutions with a Varian Cary Eclipse fluorescence spectrophotometer. UV–vis and fluorescence spectra were recorded using standard 1 cm quartz cells at room temperature. Toluene of spectroscopic grade (Aldrich) was used to prepare the solutions. The

• compounds 5a–c in toluene before irradiation (no emission) and c) during irradiation (photoluminescence, λex = 365 nm) at room temperature. UV–vis (solid lines) and fluorescence emission (dashed, λex = 365 nm) spectra of compounds 6a,b in toluene (c = 2 10−5 M, l = 1 cm) at room temperature. UV–vis

Elucidating the glycan-binding specificity and structure of Cucumis melo agglutinin, a new R-type lectin

• Jon Lundstrøm,
• Emilie Gillon,
• Valérie Chazalet,
• Nicole Kerekes,
• Antonio Di Maio,
• Ten Feizi,
• Yan Liu,
• Annabelle Varrot and
• Daniel Bojar

Beilstein J. Org. Chem. 2024, 20, 306–320, doi:10.3762/bjoc.20.31

• supplier instructions (New England Biolabs, #T1020S) and ligation using the DNA ligation kit, Mighty Mix (Ozyme, Takara, #TAK6023Z), at room temperature to form the pET40b-TEV-CMA11 plasmid. The N-terminal domain of CMA1 (6–132 in mature protein) was amplified by PCR using the following primers: forward

• 1 μL of Denarase® (C-LEcta GmbH, #20804) and moderate agitation on a rotating wheel for a period of 30 min at room temperature, cells were lysed using a cell disruptor (Constant Systems Ltd, UK) under a pressure of 2.5 kbar. The lysate was cleared by centrifugation at 24,000g for 30 min at 4 °C and

• equal volume of the sample, and the mixture was incubated for 60 min at room temperature. Starting concentrations were: CMA1 0.6 mg/mL, AAL 0.5 mg/mL, ConA 2.5 mg/mL, RCA1 2.5 mg/mL, and SNA 0.5 mg/mL. Thermal shift assay Thermal shift assays were performed using a Mini Opticon Real Time PCR machine

Synthesis of π-conjugated polycyclic compounds by late-stage extrusion of chalcogen fragments

• Aissam Okba,
• Pablo Simón Marqués,
• Kyohei Matsuo,
• Naoki Aratani,
• Hiroko Yamada,
• Gwénaël Rapenne and
• Claire Kammerer

Beilstein J. Org. Chem. 2024, 20, 287–305, doi:10.3762/bjoc.20.30

• room temperature, other group-16 heteropines suffer from thermal instability. Indeed, the low activation barrier for S, Se or Te cheletropic extrusion from the norcaradiene valence isomer, combined with the irreversibility of this process, shifts the tautomerization equilibrium and delivers benzene as

• the corresponding planar HBC at room temperature upon acidic treatment under air, thus triggering SeO-elimination as well as cyclodehydrogenation in a single step. As mentioned above, oxepine derivatives display higher stability compared to other chalcogen heteropines and direct oxygen extrusion from

• voltammetry studies revealed that reduction of dinaphthooxepine 33 proceeds irreversibly, giving rise to a new chemical species (Figure 2), and this was further confirmed by chemical reduction in the presence of decamethylcobaltocene CoCp*2 at room temperature. Using two equivalents of this 1-electron

Synthesis of spiropyridazine-benzosultams by the [4 + 2] annulation reaction of 3-substituted benzoisothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes

• Wenqing Hao,
• Long Wang,
• Jinlei Zhang,
• Dawei Teng and
• Guorui Cao

Beilstein J. Org. Chem. 2024, 20, 280–286, doi:10.3762/bjoc.20.29

• ketimine and its subsequent [4 + 2] annulation reaction with 1,2-diaza-1,3-diene in the presence of Et3N (2.0 equiv) in diethyl ether at room temperature (Table 1, entry 1). However, no product was detected under these conditions. We then replaced diethyl ether with toluene, which resulted in the desired

Nucleophilic functionalization of thianthrenium salts under basic conditions

• Xinting Fan,
• Duo Zhang,
• Xiangchuan Xiu,
• Bin Xu,
• Yu Yuan,
• Feng Chen and
• Pan Gao

Beilstein J. Org. Chem. 2024, 20, 257–263, doi:10.3762/bjoc.20.26

• in 88% yield under the following optimal conditions: S-(alkyl)thianthrenium salt 1a and 4-bromothiophenol (2a) as the model substrates, N,N-diisopropylethylamine (DIPEA) as the base, were added to a vessel in air; after stirring for 16 hours at room temperature, the corresponding product was isolated

• using nucleophiles directly, without the need for an external metal catalyst. Synthetic application of thianthrenium salts. Substrate scope. Reaction conditions: alkylthianthrenium salts 1 (0.3 mmol), thiophenols 2 (0.2 mmol), DIPEA (0.4 mmol) in 2.0 mL of MeCN at room temperature for 16 h under air

Substitution reactions in the acenaphthene analog of quino[7,8-h]quinoline and an unusual synthesis of the corresponding acenaphthylenes by tele-elimination

• Ekaterina V. Kolupaeva,
• Narek A. Dzhangiryan,
• Alexander F. Pozharskii,
• Oleg P. Demidov and
• Valery A. Ozeryanskii

Beilstein J. Org. Chem. 2024, 20, 243–253, doi:10.3762/bjoc.20.24

• 5Н+PicO−, in the cationic part of which a similar intramolecular NHN hydrogen bond is realized [15]. To understand the structure of the resulting complex, we tried to grow its crystals from acetonitrile by co-evaporating solutions of quinoline 5 and chloranil at room temperature. Interestingly, in

• positions 5 and 8 already at room temperature (Scheme 3). The overall yield of the main product 10 turned out to be high, but the substance contained a hard-to-separate impurity in an amount of up to 12%, to which, judged by the high-field position of the signals in the corresponding proton spectrum, was

• , dipyridoacenaphthene 5 is not brominated by molecular bromine in chloroform or acetic acid. The action of the NBS–DMF system, previously proposed for the electrophilic bromination of alkylaromatic compounds [26], leaves substrate 5 unchanged at room temperature, and when heated to 75 °C for several days causes its

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• underwent E–Z photoisomerization in benzene upon irradiation with yellow light and returned to E-isomer in darkness at room temperature within about 30 seconds [39]. One year later, Pummerer and Marondel attempted to reproduce this experiment and to detect the Z-isomer of N,N'-dimethylindigo 11a upon

• to the presence of the electron-withdrawing ester groups. Importantly, only the Z-form of 18c was found to be stable enough with a half-life of 2.8 min at room temperature in acetonitrile (77% of Z-isomer in PSS) and 4.1 minutes in toluene (91% of Z-isomer in PSS) after irradiation with red light

• , extending from 0.48 seconds to 22 hours at room temperature due to formation of the long-living intramolecular dimeric species. Photochromic N,N'-diacylindigos After the initial report on the photochromic behavior of N,N'-diacetylindigo (9a) in 1954 [37], Wyman and Zenhäusern continued spectroscopic studies

Optimizations of lipid II synthesis: an essential glycolipid precursor in bacterial cell wall synthesis and a validated antibiotic target

• Milandip Karak,
• Cian R. Cloonan,
• Brad R. Baker,
• Rachel V. K. Cochrane and
• Stephen A. Cochrane

Beilstein J. Org. Chem. 2024, 20, 220–227, doi:10.3762/bjoc.20.22

• conditions such as transitioning from 0 °C to room temperature and extending the reaction duration from 3 to 24 hours, we did not observe the anticipated enhancements (51% yield, entry 1, Table 1). This trend persisted when we attempted glycosylation between C6-acetylated MurNAc derivative 2b and 1a, where

• observations, we initially noted that at room temperature, the degradation rate of glycosyl donor 1a exceeded the rate of product formation. This led to a complex mixture consisting of the target product 3a, acceptor 2a, and various degraded products of donor 1a. This situation posed challenges, as even

Copper-catalyzed multicomponent reaction of β-trifluoromethyl β-diazo esters enabling the synthesis of β-trifluoromethyl N,N-diacyl-β-amino esters

• Youlong Du,
• Haibo Mei,
• Ata Makarem,
• Ramin Javahershenas,
• Vadim A. Soloshonok and
• Jianlin Han

Beilstein J. Org. Chem. 2024, 20, 212–219, doi:10.3762/bjoc.20.21

• General procedure for copper-catalyzed multicomponent reaction of β-amino esters Into a flask were added amines 1 (0.4 mmol), acids 3 (0.1 mmol), CuI (20 mol %), and CH3CN (2 mL). Then, the mixture was stirred at room temperature under a nitrogen atmosphere and t-BuONO (0.4 mmol) was added dropwise

• . Stirring was continued at room temperature for 2.5 h and the solvent was removed in vacuum. Products 4 were purified on a TLC plate of 20 cm × 20 cm using petroleum ether/ethyl acetate 7:1 (v/v) as eluent. Mumm-type rearrangement of diazo compounds. Substrate scope study of this Cu-catalyzed reaction

• side reactions was carried out with benzyl 3-amino-4,4,4-trifluorobutanoate (1a) and benzoic acid (3a) as model substrates. The initial reaction of amine 1a and acid 3a in acetonitrile in the presence of diazotization reagent tert-butyl nitrite with CuI (10 mol %) as catalysts for 2.5 h at room

Chiral phosphoric acid-catalyzed transfer hydrogenation of 3,3-difluoro-3H-indoles

• Yumei Wang,
• Guangzhu Wang,
• Yanping Zhu and
• Kaiwu Dong

Beilstein J. Org. Chem. 2024, 20, 205–211, doi:10.3762/bjoc.20.20

• (1a) as the model substrate, Hantzsch ester (HE-Et) as the hydrogen source, and BINOL-derived chiral phosphoric acids (CPA) as the catalyst (Table 1). With chiral phosphoric acid CPA-1, the transfer hydrogenation reaction proceeded well in PhCF3 at room temperature and the target product 2a was

• and the reaction mixture was stirred at room temperature for 3 h. After concentrating the mixture, the residue was purified by column chromatography on silica gel using a mixture of petroleum ether/ethyl acetate 30:1 (v/v) as the eluent to afford products 2. The yields were determined by 19F NMR

Metal-catalyzed coupling/carbonylative cyclizations for accessing dibenzodiazepinones: an expedient route to clozapine and other drugs

• Amina Moutayakine and
• Anthony J. Burke

Beilstein J. Org. Chem. 2024, 20, 193–204, doi:10.3762/bjoc.20.19

• relevant heterocycles in high efficiency [10]. The Chan–Lam coupling is considered a greener alternative to traditional C–N coupling reactions, as it can be carried out under mild reaction conditions (room temperature and short reaction times, etc.), plus it does not require expensive metals like Pd, being

• molecular sieves 3 Å. The reaction was left stirring at room temperature for several hours, and monitored by TLC. After consumption of the starting material (verified through TLC), the reaction mixture was filtered through a celite pad to remove the residual catalyst and molecular sieves. The volatiles were

• equiv, 0.19 mmol), and Et3N (0.026 mL, 0.19 mmol) were added. The reaction mixture was then stirred at 130 °C under a nitrogen atmosphere. After completion of the reaction, as determined by TLC, the reaction mixture was allowed to cool to room temperature. The mixture was filtered through a pad of

Comparison of glycosyl donors: a supramer approach

• Anna V. Orlova,
• Nelly N. Malysheva,
• Maria V. Panova,
• Nikita M. Podvalnyy,
• Michael G. Medvedev and
• Leonid O. Kononov

Beilstein J. Org. Chem. 2024, 20, 181–192, doi:10.3762/bjoc.20.18

• dried at 80 °C in vacuo (0.1 Torr, 1 h)) was added. The mixture was stirred at room temperature (≈20 °C) until complete consumption of the starting material (TLC monitoring, Rf = 0.10 (7), Rf = 0.57 (2), benzene/EtOAc 9:1). The reaction mixture was concentrated under reduced pressure, the residue was

• previously [33]. The residue was dissolved in anhydrous MeOH (3 mL per 0.1 mmol of sialyl donor) and MeONa (0.3 mL of 1 M solution in MeOH per 0.1 mmol of sialyl donor) followed by ethyl trifluoroacetate (0.1 mL per 0.1 mmol of sialyl donor) was added. The reaction mixture was kept at room temperature

• . The reaction mixture was kept at room temperature overnight, then quenched by addition of methanol (3 mL), and concentrated under reduced pressure. The residue was co-concentrated with toluene (3 mL), dissolved in CH2Cl2 (40 mL), washed with water (40 mL), the organic layer was filtered through a

Synthesis of the 3’-O-sulfated TF antigen with a TEG-N₃ linker for glycodendrimersomes preparation to study lectin binding

• Mark Reihill,
• Hanyue Ma,
• Dennis Bengtsson and
• Stefan Oscarson

Beilstein J. Org. Chem. 2024, 20, 173–180, doi:10.3762/bjoc.20.17

• molecular sieves (10.2 g) were added and the resulting suspension was stirred at room temperature for 16 hours. NIS (6.66 g, 29.6 mmol) and AgOTf (760 mg, 2.96 mmol) were then added, and the reaction was stirred at room temperature for 40 minutes. The reaction was then quenched with Et3N, filtered through

• )-α-ᴅ-galactopyranoside (5): Compound 4 (8.65 g, 12.5 mmol) was placed under N2 and dissolved in dry MeOH (250 mL). NaOMe (68 mg, 1.3 mmol) was added, and the reaction was stirred at room temperature for 4 hours. The solution was then neutralised with Amberlite® IR120 (H+ form) resin, filtered and

• -300 4 Å molecular sieves (5.45 g) were added, and the resulting suspension was stirred at room temperature for 23 hours. NIS (5.23 g, 23.2 mmol) and AgOTf (577 mg, 2.25 mmol) were added, and the reaction was stirred at room temperature for 1 hour. Et3N was then added until the pH became neutral, and

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

• + 2] CA–RE reaction is extremely slow when applied to mono-substituted alkynes bearing an DMA group. Conversely, for bis-substituted alkynes, the reaction occurs readily at room temperature, yielding the corresponding TCBD products, as shown in Scheme 2. This reaction required the presence of two

• agent for TCNE. Anthracene-based ynamide 16 offers two potential reactive sites for TCNE, one residing at the anthracene moiety and other at the alkyne moiety, as shown in Scheme 9 [71]. As exemplified by Trolez et al., the introduction of one equivalent of TCNE to 16 at room temperature initiates a [4

• substituents on the alkynes. The remarkable reactivity displayed by angle-strained alkynes makes them highly valuable tools in biorthogonal chemistry [107][108][109]. The reaction between dibenzo-fused cyclooctyne 20 and TCNE was observed to occur at room temperature, quantitatively yielding 22, wherein the