(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

• tetrasubstituted BCHs was recently reported by Shi and co-workers [82]. They employed Hantzsch esters as catalysts in the [2π + 2σ] cycloaddition of alkenes and bicyclobutanes. The synthesis of bicyclohexyl ketones by formal (3 + 2) cycloaddition of bicyclobutane and ketenes was recently reported by Studer and co

(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

• out. In this case, a mixture of 2-chloro-1,1,1,4,4,4-hexafluorobut-2-enes (6a,b) and 2-iodo-1,1,1,4,4,4-hexafluorobut-2-enes (7a,b) in a ratio of 3:2 was formed from the concurrent elimination reactions of hydrogen iodide and hydrogen chloride (Scheme 5). The chloro- and iodobutenes were separated by

• and previously unknown product 11 were also recorded in the reaction mixture (Scheme 7). The 19F NMR spectrum of compound 11 showed two signals at −65.6 and −99.1 ppm in a ratio of 3:2 and in the 1H NMR spectrum, a multiplet at 6.5 ppm was detected. Based on the received data, we assumed that product

• of allene resulted in the formation of (Z)-1,2-dibromo-1,1,4,4,4-pentafluorobut-2-ene (13) in 92% yield, which was isolated as a colorless liquid and fully characterized by NMR spectroscopy (Scheme 10). The 19F NMR spectrum showed two signals with the integrated intensity ratio 3:2, a doublet for a

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

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

• ketimines as suitable three-carbon synthons in [3 + 2] and [3 + 3] annulations [11][12][13][14][15]. However, methods using N-sulfonyl ketimines as dienophiles in [4 + 2] annulation reactions to afford biologically important spiro compounds are still limited to date [16]. 1,2-Diaza-1,3-dienes [17][18][19

Catalytic multi-step domino and one-pot reactions

• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2024, 20, 254–256, doi:10.3762/bjoc.20.25

• . Zhang, Ma, and W. Zhang reflects the state of the art in the α-amino acid-based [3 + 2] cycloaddition reactions of N–H-type azomethine ylides in multicomponent, one-pot, and stepwise reactions for the synthesis of diverse bioactive heterocyclic compounds and natural products [9]. Computational studies

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

• Celite® and concentrated in vacuo. The resulting residue was taken up in EtOAc (700 mL) and washed with 10% aq Na2S2O3 (700 mL), water (700 mL) and brine (700 mL). The organic phase was then dried over MgSO4, filtered and reduced to dryness. Flash chromatography on silica gel (toluene→toluene/EtOAc, 3:2

• concentrated under reduced pressure. Flash chromatography on silica gel (toluene→toluene/acetone, 7:3) yielded 5 as a gold-coloured syrup (7.83 g, 96%). Rf = 0.4 (toluene/EtOAc, 3:2); [α]D +67 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) δ 5.58 (d, J = 9.8 Hz, 1H, NH), 4.93 (d, J = 3.6 Hz, 1H, H-1), 4.77 (d, J

• )ethoxy]ethyl 2,3,4,6-tetra-O-acetyl-β-ᴅ-galactopyranosyl-(1→3)-2-deoxy-4,6-O-di-tert-butylsilylene-2-(2’2’2’-trichloroethoxycarbonylamino)-α-ᴅ-galactopyranoside (7): Donor 6 [16] (7.67 g, 17.4 mmol) and acceptor 5 (7.57 g, 11.6 mmol) were placed under N2 together and dissolved in dry CH2Cl2 (230 mL). AW

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

• reactions, yielding multicyanated ethenes [95]. Contrarily, alkenes bearing three or four ester substitutions partake in a [4 + 2]-type hetero-Diels–Alder (DA) reaction, yielding a third product, presumably through a [3 + 2] cycloaddition reaction, followed by rearrangement. The [2 + 2] CA–RE reactions

• equivalents of TCNEO relative to the alkyne substrate for the generation of the TCBD products [100]. For the reaction, the formal [3 + 2] cycloaddition reaction is postulated to initiate through the initial nucleophilic attack of the alkyne carbon on the electrophilic TCNEO carbon, yielding a zwitterionic

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

• Nedra Touj,
• François Mazars,
• Guillermo Zaragoza and
• Lionel Delaude

Beilstein J. Org. Chem. 2023, 19, 1947–1956, doi:10.3762/bjoc.19.145

• system (G) was first investigated by Albrecht et al. in 2008 [23]. Because the heterocyclic precursors needed to prepare 1,2,3-triazol-5-ylidenes are readily available through the [3 + 2] cycloaddition of an azide and an alkyne, these compounds are currently the most popular MICs for catalytic and other

• -disubstituted-1,2,3-triazole derivatives is readily achieved via the copper(I)-catalyzed [3 + 2] cycloaddition of an azide and a terminal alkyne (CuAAC) [63][64][65]. A further alkylation of the N3 position with an alkyl halide is an equally straightforward procedure that ultimately affords a large assortment

Construction of diazepine-containing spiroindolines via annulation reaction of α-halogenated N-acylhydrazones and isatin-derived MBH carbonates

• Xing Liu,
• Wenjing Shi,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2023, 19, 1923–1932, doi:10.3762/bjoc.19.143

• spirooxindoles [36][37][38][39][40][41][42][43]. In the presence of Lewis bases, isatin-derived MBH carbonates usually undergo [3 + 2] and [3 + 3] cycloaddition reactions with a broad range of active C–C and C–N double bonds and 1,3-dipolarpohiles to give various five- or six-membered cyclic spirooxindoles [44

Beyond n-dopants for organic semiconductors: use of bibenzo[d]imidazoles in UV-promoted dehalogenation reactions of organic halides

• Kan Tang,
• Megan R. Brown,
• Chad Risko,
• Melissa K. Gish,
• Garry Rumbles,
• Phuc H. Pham,
• Oana R. Luca,
• Stephen Barlow and
• Seth R. Marder

Beilstein J. Org. Chem. 2023, 19, 1912–1922, doi:10.3762/bjoc.19.142

• been used by Murphy’s group and others for a variety of transformations, such as the formation of indolines from N-allyl-2-iodoanilines [1], indanones from 3-(2-halophenyl)propanoic esters [2][3], and 3-methyl-2,3-dihydrobenzofuran from 1-allyloxy-2-halobenzenes [4]. Related species have also been used

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• notable advantages in terms of both step- and atom-economy. Taking inspiration from the groundbreaking work of Shang and Fu [6], Li and colleagues demonstrated an innovative approach for the photocatalytic [3 + 2] and [4 + 2] annulation of enynals 32 and γ,σ-unsaturated N-(acyloxy)phthalimides 33 (Scheme

• of fused ketones 34, eliminating the need for transition-metal catalysts or oxidants. The technique offered a broad substrate scope, remarkable selectivity, and simple reaction conditions. A plausible mechanism had been proposed for the photocatalytic decarboxylative [3 + 2]/[4 + 2] annulation, as

• alkylation employing ammonium iodide. NaI/PPh3/CuBr cooperative catalysis for photocatalytic C(sp3)–O/N cross-coupling reactions. Proposed mechanism of NaI/PPh3/CuBr cooperative catalysis for photocatalytic C(sp3)–O/N cross-couplings. Photocatalytic decarboxylative [3 + 2]/[4 + 2] annulation between enynals

Trifluoromethylated hydrazones and acylhydrazones as potent nitrogen-containing fluorinated building blocks

• Zhang Dongxu

Beilstein J. Org. Chem. 2023, 19, 1741–1754, doi:10.3762/bjoc.19.127

• presence of Brønsted acid. In their pioneering research, Tanaka et al. reported the [3 + 2] cycloaddition reactions of trifluoroacetaldehyde hydrazones and glyoxals to give 4-hydroxy-3-trifluoromethylpyrazoles. The resultant pyrazoles containing a free 4-hydroxy group were easily converted to a variety of

• regioselective [3 + 2] cycloadditions [59][60][61][62][63] (Scheme 10a). Similarly, trifluoroacetonitrile imine reacted with mercaptoacetaldehyde and mercaptocarboxylic acids to generate fluorinated 1,3,4-thiadiazines with good yields via a [3 + 3] annulation [64] (Scheme 10b). Meanwhile, mercaptoacetaldehyde as

• group has attracted a significant level of attention, and many trifluoromethylated pyrazoles have been used in medicinal products or in pesticides [66]. The [3 + 2] cycloaddition reactions are considered among the most powerful tools for the synthesis of versatile fluoroalkylated pyrazoles. Enol ethers

Unprecedented synthesis of a 14-membered hexaazamacrocycle

• Anastasia A. Fesenko and
• Anatoly D. Shutalev

Beilstein J. Org. Chem. 2023, 19, 1728–1740, doi:10.3762/bjoc.19.126

• was filtered and washed with cold DMF (3 × 2 mL). The 1H NMR spectrum showed that the solid was pure macrocycle 5. The mother liquor was collected, H2O (20 mL) was added and the solution was left standing overnight at room temperature. After that, some additional violet crystals precipitated and were

Decarboxylative 1,3-dipolar cycloaddition of amino acids for the synthesis of heterocyclic compounds

• Xiaofeng Zhang,
• Xiaoming Ma and
• Wei Zhang

Beilstein J. Org. Chem. 2023, 19, 1677–1693, doi:10.3762/bjoc.19.123

• Pharmacy, Changzhou University, Changzhou 213164, China 10.3762/bjoc.19.123 Abstract The [3 + 2] cycloadditions of stabilized azomethine ylides (AMYs) derived from amino esters are well-established. However, the reactions of semi-stabilized AMYs generated from decarboxylative condensation of α-amino acids

• with arylaldehydes are much less explored. The [3 + 2] adducts of α-amino acids could be used for a second [3 + 2] cycloaddition as well as for other post-condensation modifications. This article highlights our recent work on the development of α-amino acid-based [3 + 2] cycloaddition reactions of N–H

• -type AMYs in multicomponent, one-pot, and stepwise reactions for the synthesis of diverse heterocycles related to some bioactive compounds and natural products. Keywords: [3 + 2] cycloaddition; decarboxylation; 1,3-dipolar; double cycloaddition; one-pot synthesis; multicomponent reaction; semi

Sulfur-containing spiroketals from Breynia disticha and evaluations of their anti-inflammatory effect

• Ken-ichi Nakashima,
• Naohito Abe,
• Masayoshi Oyama,
• Hiroko Murata and
• Makoto Inoue

Beilstein J. Org. Chem. 2023, 19, 1604–1614, doi:10.3762/bjoc.19.117

• fractions were pooled by TLC analysis to yield four combined fractions (Frs. B1–B4). Fr. B2 was further separated on an ODS column eluted with MeOH/H2O (stepwise gradient of 2:3, 1:1, 3:2, and 1:0, v/v) to yield four combined subfractions. The second subfraction was separated by silica gel CC with ethyl

Morpholine-mediated defluorinative cycloaddition of gem-difluoroalkenes and organic azides

• Tzu-Yu Huang,
• Mario Djugovski,
• Sweta Adhikari,
• Destinee L. Manning and
• Sudeshna Roy

Beilstein J. Org. Chem. 2023, 19, 1545–1554, doi:10.3762/bjoc.19.111

• plausible pathways. Attractive elements include the regioselective and straightforward direct synthesis of fully substituted 1,2,3-triazoles, which are otherwise difficult to access, from readily available starting materials. Keywords: [3 + 2] cycloaddition; defluorination; fully decorated 1,2,3-triazoles

• are available [2][3], only a couple of cycloaddition reactions has been reported [4]. For example, [3 + 2] dipolar cycloadditions to form saturated difluoroisoxazolidines [5][6] and difluoropyrrolidines [7] and [4 + 2] cycloaddition reactions with gem-difluoro-1,3-dienes [8]. The overall landscape of

• generated via an azide–alkyne cycloaddition or a multicomponent reaction between carbonyls and azides [17]. α-Trifluoromethyl (α-CF3) carbonyls were recently utilized to generate NH-1,2,3-triazoles and fully substituted 1,2,3-triazoles [28][29]. However, there are no reports of a formal [3 + 2

Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• diversity, low cost, and versatile applications. This article overviews applications of NHC–Cu(I) complexes as catalysts in organic synthesis over the last 12 years, which include hydrosilylation reactions, conjugate addition, [3 + 2] cycloaddition, A3 reaction, boration and hydroboration, N–H and C(sp2)–H

• addition; [3 + 2] cycloaddition reaction; hydrosilylation reaction; N-heterocyclic carbenes; NHC–Cu complexes; NHC–Cu complexes as catalyst; Introduction N-Heterocyclic carbenes (NHCs) are a neutral species having the carbene carbon atom as a part of the nitrogen heterocyclic ring. The transient

• yield by reacting [Cu(CH3CN)4]BF4 with 2 equiv of benzimidazolium salt 38 in the presence of NaOt-Bu (Scheme 14) [28]. The catalytic activity of the complex 39 was studied in the [3 + 2] cycloaddition of azides with alkynes [28]. Coyle et al. reported the synthesis of a series of NHC and ADC (acyclic

One-pot nucleophilic substitution–double click reactions of biazides leading to functionalized bis(1,2,3-triazole) derivatives

• Hans-Ulrich Reissig and
• Fei Yu

Beilstein J. Org. Chem. 2023, 19, 1399–1407, doi:10.3762/bjoc.19.101

• azide was combined with a subsequent copper-catalyzed (3 + 2) cycloaddition with terminal alkynes. This one-pot process was developed with a simple model alkyne, but then applied to more complex alkynes bearing enantiopure 1,2-oxazinyl substituents. Hence, the precursor compounds 1,2-, 1,3- or 1,4-bis

• discovery of the copper-catalyzed alkyne azide (3 + 2) cycloaddition (CuAAC) [3][4], has dramatically changed the approaches to many problems in chemistry, supramolecular chemistry, materials science, biological chemistry and related fields (selected reviews: [5][6][7][8][9][10][11][12][13][14][15

• the Nobel Prize in 2022 to M. Meldal, K. B. Sharpless and C. R. Bertozzi did not come as a surprise. In most cases the (3 + 2) cycloadditions were performed with isolated (and purified) organic azides, but it was early found that one-pot processes generating the potentially hazardous azides [22] in

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• oxidizing this radical to the corresponding cation. In the presence of Et3N, [FeIII(btz)3]3+ is reductively quenched after excitation to its 2LMCT excited state to generate [FeII(btz)3]2+ (equivalent to PC•− in the classical conPET mechanism) (Figure 20C). [FeII(btz)3]2+ is excited again to the more

• radical. This is strongly supported by a single turnover experiment, where exclusive excitation of [FeII(btz)3]2+ with 700 nm LEDs after in situ generation and substrate addition in the dark generated 5% of product even with only 0.5 mol % of catalyst present. In its ground state, [FeII(btz)3]2+ is not

• reducing enough to engage the model substrate perfluorooctyl iodide and instead *[FeII(btz)3]2+ was verified as the key catalytic species by transient absorption spectroscopy; even though the strongly reducing α-amino alkyl radical intermediate might also engage in the reduction of alkyl halides or act as

Synthesis of tetrahydrofuro[3,2-c]pyridines via Pictet–Spengler reaction

• Elena Y. Mendogralo and
• Maxim G. Uchuskin

Beilstein J. Org. Chem. 2023, 19, 991–997, doi:10.3762/bjoc.19.74

• underwent abundant tarring (Table 1, entries 17 and 19). The treatment of the reaction mixture after the reaction with an aqueous solution of NaHCO3 turned out to be less effective (Table 1, entry 20). It should be noted that 3-(2-oxopropyl)-2-phenylpiperidin-4-one (5a), which is a product of further acid

• optimized reaction conditions, in addition to the desired tetrahydrofuro[3,2-c]pyridine (4h), led to the major formation of the corresponding 1,4-diketone 5h. This unexpected formation of 3-(2-oxopropyl)piperidin-4-one (5h) led us to the idea that the tandem sequence Pictet–Spengler cyclization/furan acid

• hydrolysis could be a convenient tool for the synthesis of substituted 3-(2-oxopropyl)piperidin-4-ones 5. Using tetrahydrofuro[3,2-c]pyridine 4a as the model compound, we studied the effect of various Brønsted acids, temperature, concentrations, and the nature of the solvent on the efficiency of the reaction

Synthesis of medium and large phostams, phostones, and phostines

• Jiaxi Xu

Beilstein J. Org. Chem. 2023, 19, 687–699, doi:10.3762/bjoc.19.50

• palladium-catalyzed intramolecular arylation of 3-(2-bromophenyl)propyl alkylphosphinates 61 approached the synthesis of 3,4,5-trihydrobenzo[c][1,2]oxaphosphepine 1-oxides 62 in moderate 39–45% yields in the presence of triethylamine in dry toluene at 100 °C [33]. When the substrates were extended to 5

• -oxaphosphepane 2-oxides, and 1,2-oxaphosphocine 2-oxides from hydrogen methyl alk-4/5-ynylphosphonates. Synthesis of 1,2-azaphosphepane 2-oxide and its benzo derivatives from 5-bromohex-5-en-1-yl methylphosphinate and 3-(2-bromophenyl)propyl alkylphosphinates. Synthesis of 4-phenyl-1,2-dihydronaphtho[2,1-c][1,2

Cassane diterpenoids with α-glucosidase inhibitory activity from the fruits of Pterolobium macropterum

• Sarot Cheenpracha,
• Ratchanaporn Chokchaisiri,
• Lucksagoon Ganranoo,
• Sareeya Bureekaew,
• Thunwadee Limtharakul and
• Surat Laphookhieo

Beilstein J. Org. Chem. 2023, 19, 658–665, doi:10.3762/bjoc.19.47

• fruits of P. macropterum (0.2 kg) were ground and soaked with MeOH (3 × 2 L) at room temperature for 3 days. The solvent was evaporated under reduced pressure at 40 °C, affording MeOH extract (10.5 g). The extract was subjected to silica gel column chromatography (CC) (70–230 mesh, 2 × 60 cm) eluting

Nucleophile-induced ring contraction in pyrrolo[2,1-c][1,4]benzothiazines: access to pyrrolo[2,1-b][1,3]benzothiazoles

• Ekaterina A. Lystsova,
• Maksim V. Dmitriev,
• Andrey N. Maslivets and
• Ekaterina E. Khramtsova

Beilstein J. Org. Chem. 2023, 19, 646–657, doi:10.3762/bjoc.19.46

• -benzothiazol-2-yl(diazo)acetates (Scheme 1, entry 3) [12], dearomative [3 + 2] cycloaddition reactions of benzothiazoles with cyclopropanes (Scheme 1, entry 4) [13][14][15], multicomponent reactions (MCRs) of benzothiazoles, isocyanides and 2-methylidenemalonates (Scheme 1, entry 5) [16], 1,3-dipolar

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• been shown to impart high levels of enantioselectivity for these ketones [46]. We performed the conjugate addition for 2 h and then added imine 58 having a tosyl protecting group. The workup allowed the isolation of domino products 59 as a mixture of diastereomers with dr 3:2 and enantiomeric purities

C3-Alkylation of furfural derivatives by continuous flow homogeneous catalysis

• Grédy Kiala Kinkutu,
• Catherine Louis,
• Myriam Roy,
• Juliette Blanchard and
• Julie Oble

Beilstein J. Org. Chem. 2023, 19, 582–592, doi:10.3762/bjoc.19.43

• initiated when the system reaches a steady state, based on the dispersion curves given by the apparatus. After reaching the steady state an aliquot of the product was taken for 1H NMR analysis using p-dinitrobenzene as an internal standard. 3-(2-(Triethoxysilyl)ethyl)furan-2-carbaldehyde (2a) The reaction