On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• [158]. The synthesis started with a cyclopentene derivative, obtained after two steps from a diol via tosylation/displacement strategy with Me2CuLi·LiI. Then, after a Lewis acid-promoted cycloaddition, the alkylation of the α-carbon atom followed by regioselective Baeyer–Villiger oxidation provided the

• ] and batteries [174]. Due to its accessibility, it is well explored in catalysis for many fields, such as cycloaddition reactions [175], polymerization [176], and C–C cross-coupling methods [177]. Several biologically active compounds have been obtained through cobalt catalysis [178][179][180

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• conjugative transformations, such as azide–alkyne [3 + 2]-cycloaddition [30][31][32][33][34][35][36][37]. Based on their previous late-stage fluorination studies [22][25], Groves et al. further showcased a manganese(III)–salen-catalyzed azidation process using an aqueous azide solution as a convenient azide

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• industry. The current review aims to cover a wide literature survey of numerous synthetic strategies. Recent reports (2017–2021) in the field of 1,4,5-trisubstituted 1,2,3-triazoles are emphasized in this current review. Keywords: azides; Click reaction; [3 + 2]‐cycloaddition; fully functionalized 1,2,3

• applications of these five-membered N-heterocycles are the result of both their easy synthetic procedures and ring functionalization [9][31][32]. Typically, 1,2,3-triazole derivatives are prepared via a 1,3-dipolar cycloaddition reaction between azides and alkynes [33]. It is worth noting that the metal

• -catalyzed Huisgen cycloaddition reaction could provide disubstituted 1,2,3-triazoles. The selective introduction of substituents to three different positions on the 1,2,3-triazole frame can notably improve the features of the molecule. Therefore, practical and cost-effective strategies for the selective

Chemical synthesis of C6-tetrazole ᴅ-mannose building blocks and access to a bioisostere of mannuronic acid 1-phosphate

• Eleni Dimitriou and
• Gavin J. Miller

Beilstein J. Org. Chem. 2021, 17, 1527–1532, doi:10.3762/bjoc.17.110

• mannuronic acid building blocks, appropriately modified at the carboxylate C6 position with a bioisosteric tetrazole. Thioglycosides containing a protected C6-tetrazole are accessed from a C6-nitrile, through dipolar cycloaddition using NaN3 with n-Bu2SnO. We also demonstrate access to orthogonally C4

• yield of 50% (compared to 31% in accessing 9 from 7). Nitrile 16 then underwent dipolar cycloaddition with NaN3, converting it to C6-tetrazole thioglycoside 17 in 55% yield. This material was then protected at tetrazole nitrogen in 76% yield using PMBCl to give 18 and 19 (N1-PMB/N2-PMB = 1:1.2) as

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• spirocyclic 1,4,2-dioxazole derivatives [13][14]. Furthermore, for photochemically generated benzonitrile isopropanide, competitive C=O and C=C additions with 1,4-quinones were observed [15]. On the other hand, the slightly less polar benzonitrile benzylide underwent [3 + 2]-cycloaddition to the C=C bond

• reported in the 1960s [17]. The latter 1,3-dipole was generated thermally from the respective tetrazole derivative 3, and the observed [3 + 2]-cycloadditions occurred chemoselectively to provide fused pyrazoles of the type 4 as exclusive products (Scheme 1). This type of cycloaddition attracted

• -thiadiazoles as the products of [3 + 2]-cycloaddition to the C=S bond [25]. Taking into account that fluorinated heterocycles [31][32][33][34], including pyrazoles [31][35][36], are of great significance for various medicinal and agricultural applications, the development of new methods for the construction of

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

• Premansh Dudhe,
• Mena Asha Krishnan,
• Kratika Yadav,
• Diptendu Roy,
• Krishnan Venkatasubbaiah,
• Biswarup Pathak and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2021, 17, 1453–1463, doi:10.3762/bjoc.17.101

• alkaloid ingenine B [20]. The iodine-catalyzed [3 + 3] cycloaddition of indolyl alcohol to enaminones [21] and the thiourea-catalyzed iso-Pictet–Spengler reaction of isotryptamine with aldehydes [22], are some noteworthy contributions to the field. A cascade or domino reaction is an interesting approach

• , alkyl N-arylideneglycinates have attracted much attention in recent years. For instance, the metal-catalyzed asymmetric [3 + 2] cycloaddition of ethyl N-benzylideneglycinates with electron-deficient alkenes has been reported to yield substituted pyrrolidines [30]. Recently, we reported the synthesis of

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

• -ethynylpyrene (40) under copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction conditions to yield the double-headed nucleoside 41 (Scheme 10) [23]. The double-headed nucleoside 41 was phosphitylated and then incorporated into oligonucleotides and was found to form highly stable DNA duplexes and three

• nucleosides were further reacted with propargylated nucleobases through a copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction followed by treatment with methanolic ammonia to give the C-3′-substituted double-headed ribofuranonucleosides 46a–c and 50a–e (Scheme 11) [36]. The double-headed nucleosides

• cycloaddition (CuAAC) reaction conditions to yield the double-headed nucleosides 154a and 154b, respectively (Scheme 39) [24]. The synthesized double-headed nucleosides 151a–d and 154a,b were phosphitylated, incorporated into oligonucleotides and characterized with respect to thermal denaturation, enzymatic

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

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• stereoselective synthesis is especially interesting, highlighting the 1,3-dipolar cycloaddition reactions with azomethine ylides as an example of transformation that take place with great stereocontrol, and allow the synthesis of polyfunctionalized pyrrolidines in a single reaction step [91][92]. On the other

• took place to the Re face of imines with (Z,SS)-configuration (Scheme 27). The cycloaddition of chiral sulfinyl imines (RS)-14 with 2-(trimethysilylmethyl)allyl acetate (91) could also be promoted by Pd(0) to give methylenepyrrolidines 92. The group of Stockman demonstrated that Pd(PPh3)4 was the best

• stereochemical outcome of the cyclization considering that the stereoinduction is derived from the dipole–dipole repulsion of the sulfinyl imine, which places the tert-butyl group on the Si face, and thus the cycloaddition occurs from the less sterically hindered Re face. The cyclization process worked also in

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• equivalents of the carbodiimide in the reaction with N,N’-disubstituted guanidines resulted in the formation of 1,2-dihydro-1,3,5-triazine derivatives as the main products of the cycloaddition reaction [82]. They also showed that increasing the amount of the carbodiimide to 3 equivalents led to excellent

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

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• -MCRs and their mechanistic insights over the past decade and shed light on its advantage over the conventional approach. Keywords: cycloaddition; Knoevenagel condensation; Michael addition; microwave; multicomponent reactions; Introduction Recently, organic chemists are focussed to develop

• [29][30], focusing on the synthetic aspect of five, six, seven and dicyclic structures. Later in 2013, Gupta et al. compiled reports of microwave-assisted cross-coupling, MCR with few cycloaddition reactions [31]. During the course of writing this review, we realized the very presence of two reviews

• enaminone B. Later, the successive Michael addition of A and enaminone B followed by an intramolecular cycloaddition with concomitant dehydration delivered the final product 7 (Scheme 2). In 2018, our research group [39] contemplated and developed an expeditious process for the synthesis of phenanthrene

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• the fact that diamine can condense with the enol substrate, forming an imine-ion intermediate absorbing in the visible region. The direct excitation of the intermediate leads to a charge-transfer excited state, completing the stereocontrolled intermolecular cycloaddition reaction with a good ratio of

• ] developed a visible-light-induced [3 + 2] cycloaddition reaction between glycine derivatives 57 and aryl epoxides 58, which can efficiently prepare a series of multisubstituted 1,3-oxazolidines 59 at room temperature (Scheme 20). The strategy can be applied smoothly to an extensive range of glycine

Synthesis of β-triazolylenones via metal-free desulfonylative alkylation of N-tosyl-1,2,3-triazoles

• Soumyaranjan Pati,
• Renata G. Almeida,
• Eufrânio N. da Silva Júnior and
• Irishi N. N. Namboothiri

Beilstein J. Org. Chem. 2021, 17, 762–770, doi:10.3762/bjoc.17.66

• synthesis of new functionalized 1,2,3-triazoles. Keywords: azoles; cycloaddition; enones; heterocycles; 1,2,3-triazoles; Introduction 1,2,3-Triazoles are significant non-natural heterocyclic scaffolds with extensive applications in biochemistry, agrochemistry and materials chemistry [1][2][3][4][5]. This

• precursors in denitrogenative transannulation reactions under metal-catalysed conditions to form other heterocycles such as functionalized pyrroles, imidazoles and pyridines (Scheme 1b) [11][12][13]. The traditional method for the synthesis of triazole unit is the Huisgen 1,3-dipolar cycloaddition between

• Meldal have independently developed a copper-catalysed azide–alkyne cycloaddition that accelerated the rate of the reaction and allowed the selective preparation of 1,5-disubstituted 1,2,3-triazoles [16][17][18][19]. As noted above, a wide range of methods are available in the literature for the

Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles

• Ramazan Koçak and
• Arif Daştan

Beilstein J. Org. Chem. 2021, 17, 719–729, doi:10.3762/bjoc.17.61

• inverse electron-demand Diels–Alder cycloaddition reactions between a dibenzosuberenone and tetrazines that bear various substituents. The pyridazines were synthesized in high yields by oxidation of dihydropyridazine-appended dibenzosuberenones with PIFA or NO. p-Quinone derivatives of pyridazines were

• obtained gave absorbance and emission at long wavelengths. Keywords: dibenzosuberenone; inverse electron-demand Diels–Alder cycloaddition reactions; p-quinone methide; polycyclic π-conjugated dihydropyridazines; pyridazines; pyrroles; Inroduction Dibenzosuberone and dibenzosuberenone derivatives are

• electron-demand Diels–Alder cycloaddition reactions of alkenes with tetrazines are commonly used for the synthesis of dihydropyridazines and pyridazines [50][51][52][53][54]. In our previous study, we made a discovery that would form the basis of a new class of dyestuffs with skeletons unlike those of

Effective microwave-assisted approach to 1,2,3-triazolobenzodiazepinones via tandem Ugi reaction/catalyst-free intramolecular azide–alkyne cycloaddition

• Maryna O. Mazur,
• Oleksii S. Zhelavskyi,
• Eugene M. Zviagin,
• Svitlana V. Shishkina,
• Vladimir I. Musatov,
• Maksim A. Kolosov,
• Elena H. Shvets,
• Anna Yu. Andryushchenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2021, 17, 678–687, doi:10.3762/bjoc.17.57

• followed by microwave-assisted intramolecular azide–alkyne cycloaddition (IAAC) gave a series of target heterocyclic compounds in moderate to excellent yields. Surprisingly, the normally required ruthenium-based catalysts were found to not affect the IAAC, only making isolation of the target compounds

• to a large number of diverse heterocyclic compounds [10][11]. Over the past decade, several cases of using an Ugi four-component reaction (Ugi-4CR) in combination with intramolecular azide–alkyne cycloaddition (IAAC) for the synthesis of 1,2,3-triazolobenzodiazepines were reported [3][7][12][13][14

• cycloaddition approach to the synthesis of 1,2,3-triazolobenzodiazepinones. Results and Discussion The development of the tandem Ugi/Click reaction approach for 1,2,3-triazolobenzodiazepinone synthesis can be logically divided into two principal parts: modification and performing synthesis of Ugi-reaction

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• Yuliya N. Biglova Department of Chemistry, Bashkir State University, 450076, Ufa, Russian Federation 10.3762/bjoc.17.55 Abstract The most common variant of fullerene core functionalization is the [2 + 1] cycloaddition process. Of these, reactions leading to methanofullerenes are the most

• compounds. The main cyclopropanating agents for the synthesis of monosubstituted methanofullerenes, the optimal conditions and the mechanism of the [2 + 1] cycloaddition, as well as the practical application of the target products are analyzed. Keywords: [2 + 1]-cycloaddition processes; analogues of [60

• discuss the primary functionalization of the fullerene core with diazo compounds to synthesize solely monosubstituted carbochain products, covers the main achievements of organic chemistry over the past 20 years in the field of [2 + 1] cycloadditions to fullerene. Review [2 + 1] Cycloaddition to C60 to

Breakdown of 3-(allylsulfonio)propanoates in bacteria from the Roseobacter group yields garlic oil constituents

• Anuj Kumar Chhalodia and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2021, 17, 569–580, doi:10.3762/bjoc.17.51

• molecule of 5 to yield 10 and 2. Alternatively, 5 can decompose to 10 and thioacroleine (14) by a Cope elimination, which explains the formation of the heterocycles 6 and 7 by dimerization through a [4 + 2] cycloaddition [5]. Compounds 6 and 7 were also reported to be formed from 5 during gas

• chromatographic (GC) analysis by an unknown mechanism [9] (7 was confused with its double bond regioisomer 3-vinyl-3,6-dihydro-1,2-dithiine (8) in this study [5]). Under these conditions the formation of the heterocyclic disulfides 7 and 8 may not involve a dimerization of 14, as a [4 + 2] cycloaddition is not a

Synthesis of N-perfluoroalkyl-3,4-disubstituted pyrroles by rhodium-catalyzed transannulation of N-fluoroalkyl-1,2,3-triazoles with terminal alkynes

• Olga Bakhanovich,
• Viktor Khutorianskyi,
• Vladimir Motornov and
• Petr Beier

Beilstein J. Org. Chem. 2021, 17, 504–510, doi:10.3762/bjoc.17.44

• electrophilic metal-bound iminocarbenes form. These iminocarbenes undergo a variety of intriguing reactions, such as a cycloaddition and a C–H functionalization, among others, leading mostly to nitrogen heterocycles [8][9][10]. Using this chemistry, a variety of pyrroles have been prepared starting from N

1,2,3-Triazoles as leaving groups: S_NAr reactions of 2,6-bistriazolylpurines with O- and C-nucleophiles

• Dace Cīrule,
• Irina Novosjolova,
• Ērika Bizdēna and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 410–419, doi:10.3762/bjoc.17.37

• of purine [73][74][75][76] or alkylation of inosine or guanosine derivatives (Ib→II, Scheme 1) [30][36]. In the next step, azide can be introduced either by a second SNAr reaction on the C2-halo derivative or by diazotization/azidation at C2. Then, the Cu(I)-catalyzed azide–alkyne cycloaddition

Diels–Alder reaction of β-fluoro-β-nitrostyrenes with cyclic dienes

• Savva A. Ponomarev,
• Roman V. Larkovich,
• Alexander S. Aldoshin,
• Andrey A. Tabolin,
• Sema L. Ioffe,
• Jonathan Groß,
• Till Opatz and
• Valentine G. Nenajdenko

Beilstein J. Org. Chem. 2021, 17, 283–292, doi:10.3762/bjoc.17.27

• a result, the corresponding norbornene 2m having a cyclopropane ring was obtained in moderate yield (44%). The cycloaddition proceeds much more slowly as a result of the high steric demand of the cyclopropyl ring of the spirodiene compared to the CH2 group of cyclopentadiene. We believe that this is

• (51.6 kJ mol−1). Whereas the entropies of activation (ΔS≠) were −181.8 and −183.1 J mol−1 K−1 for the formation of the endo and exo-isomers, respectively. The values obtained are typical for concerted [4 + 2]-cycloaddition reactions [60]. The free energies of activation () were calculated for 121.26 kJ

1,2,3-Triazoles as leaving groups in S_NAr–Arbuzov reactions: synthesis of C6-phosphonated purine derivatives

• Kārlis-Ēriks Kriķis,
• Irina Novosjolova,
• Anatoly Mishnev and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 193–202, doi:10.3762/bjoc.17.19

• chlorine at the purine C2 position by azide, and 3) copper-catalyzed azide–alkyne 1,3-dipolar cycloaddition (CuAAC) with different alkynes. Pathway B included: 1) the two-step synthesis of 2,6-bistriazolylpurine derivatives 6 from 2,6-dichloropurine derivative 1 [22] and 2) the SNAr–Arbuzov reaction with

Supramolecular polymerization of sulfated dendritic peptide amphiphiles into multivalent L-selectin binders

• David Straßburger,
• Svenja Herziger,
• Katharina Huth,
• Moritz Urschbach,
• Rainer Haag and
• Pol Besenius

Beilstein J. Org. Chem. 2021, 17, 97–104, doi:10.3762/bjoc.17.10

• structures modified with sulfate groups, and their capability to interact with biological components has been demonstrated recently [31][32]. In this work, we therefore coupled dPGS to C2-symmetrical discotic peptide amphiphiles using copper-catalyzed azide alkyne cycloaddition chemistry. The evaluation of

• , post-functionalization using a subsequent copper-catalyzed azide–alkyne cycloaddition reaction became accessible [35][36]. At the same time the other two unmodified side arms of the dendritic amphiphile make sure that the fidelity of the β-sheet motifs and directed supramolecular polymerization remains

• copper-catalyzed azide–alkyne cycloaddition (Scheme 2). The reaction took place in degassed DMSO at 50 °C with CuSO4 pentahydrate, sodium ascorbate and tris(benzyltriazolylmethyl)amine (TBTA) as chelating species. HPLC-monitoring of the reaction showed a full conversion after three days and the crude

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

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

• ] 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 progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• chemical ecology of Adalia bipunctata and the recent methodologies to obtain adaline (1), euphococcinine (2), and N-methyleuphococcinine (3). Keywords: 9-azabicyclo[3.3.1]nonane; Coccinelid beetles; dipolar cycloaddition; homotropane; ring-closing metathesis; Introduction Coccinellid beetles contain a

• forms. Key (homotropane construction) steps included: i) inter and intramolecular Mannich reaction; ii) double Michael addition in the cyclooctadienone derivative; and iii) intramolecular 1,3-dipolar cycloaddition. As shown in Scheme 1, the azabicyclononane ring is an interesting target for strategies

• dipolar cycloaddition to produce tricyclic isoxazolidines [40]. The synthesis started from 5-hexyn-1-ol (4, Scheme 2). The alcohol was treated with dihydropyran followed by alkylation using butyllithium and then, acetal deprotection, providing the alcohol 5 as a key starting compound for the (±)-adaline