Visible-light-driven NHC and organophotoredox dual catalysis for the synthesis of carbonyl compounds

• Vasudevan Dhayalan

Beilstein J. Org. Chem. 2025, 21, 2584–2603, doi:10.3762/bjoc.21.200

• ]. Scheidt and co-workers used a tandem annulation strategy, merging NHC and organic photoredox catalysis for the convergent novel synthesis of α,β-disubstituted cyclohexyl ketone scaffolds 30. This cascade process rapidly forms two contiguous C–C bonds via a formal [5 + 1] cycloaddition. It represents a

Recent advances in total synthesis of illisimonin A

• Juan Huang and
• Ming Yang

Beilstein J. Org. Chem. 2025, 21, 2571–2583, doi:10.3762/bjoc.21.199

• starting materials [32]. This synthesis features a pentafulvene-based intramolecular [6 + 2] cycloaddition [41][42] and a nitroso-Diels–Alder reaction [43] as key steps. The route began with the esterification of pentafulvenol 82 to give β-ketoester 83, which was subsequently converted to the sterically

• encumbered tricyclic lactone 84 via an intramolecular [6 + 2] cycloaddition (Scheme 8). Attempts to achieve an asymmetric version of the cycloaddition were unsuccessful. Treatment of the lactone with MeMgBr, followed by mesylation and elimination of the resulting hemiacetal, afforded enol ether 85. Reaction

• into the pentacyclic diene intermediate 93 via a two-step sequence. Subsequent [4 + 2] cycloaddition of 93 with singlet oxygen yielded an unstable endoperoxide adduct 94, which rearranged to diketone 95. A five-step sequence, featuring an intramolecular aldol reaction to assemble the pentacyclic core

Total syntheses of highly oxidative Ryania diterpenoids facilitated by innovations in synthetic strategies

• Zhi-Qi Cao,
• Jin-Bao Qiao and
• Yu-Ming Zhao

Beilstein J. Org. Chem. 2025, 21, 2553–2570, doi:10.3762/bjoc.21.198

• is as follows: Starting from the chiral compound (S)-carvone, four simple transformations yield the enone intermediate 11. This intermediate undergoes an intermolecular [4 + 2] cycloaddition with diene 12, generating two sets of regioselective products in an approximate ratio of 1:1. The product with

• reaction – a powerful method for building five-membered rings. This single [2 + 2 + 1] cycloaddition step efficiently converted a simple linear precursor into a complex bicyclic system. Subsequent late-stage modifications of the enone skeleton introduced multiple chiral centers, significantly enhancing

Rapid access to the core of malayamycin A by intramolecular dipolar cycloaddition

• Yilin Liu,
• Yuchen Yang,
• Chen Yang,
• Sha-Hua Huang,
• Jian Jin and
• Ran Hong

Beilstein J. Org. Chem. 2025, 21, 2542–2547, doi:10.3762/bjoc.21.196

• of Sciences, 345 Lingling Road, Shanghai 200032, P.R. China 10.3762/bjoc.21.196 Abstract We have streamlined a dipolar cycloaddition approach to assemble the core of malayamycin A and other related uracil nucleosides possessing the common bicyclic perhydrofuropyran framework. The latent

• development of potent fungicides. Keywords: dipolar cycloaddition; elimination; fungicide; nucleoside; oxazoline; Introduction Modern agriculture relies on various effective fungicides to combat crop diseases for achieving significant gains [1]. However, the long-term and widespread use of chemicals and

• monosaccharides and applying dipolar cycloaddition to construct various bioactive compounds [21][22][23][24][25][26][27], we intended to develop a practical strategy to access the perhydrofuropyran core of malayamycin A and other uracil nucleosides to enable future rapid derivatization (Scheme 1B). The bicyclic

Pentacyclic aromatic heterocycles from Pd-catalyzed annulation of 1,5-diaryl-1,2,3-triazoles

• Kaylen D. Lathrum,
• Emily M. Hanneken,
• Katelyn R. Grzelak and
• James T. Fletcher

Beilstein J. Org. Chem. 2025, 21, 2524–2534, doi:10.3762/bjoc.21.194

• modification of the base-catalyzed conditions reported by Kwok [53], where a stoichiometric plus additional catalytic amount of tetraethylammonium hydroxide base in DMSO solvent was used to promote tandem trimethylsilyl deprotection and cycloaddition in one preparation (Figure 3). Isolated yields of this

• tandem approach preparing 7–12 ranged from 43–85%, which were similar to running the deprotection and cycloaddition reactions sequentially. Pd-catalyzed annulation using a modification of previously reported reaction conditions [46] under microwave irradiation instead of thermal heating converted 1,5

• (right). Overview of the synthetic scheme employed by this study. Base-catalyzed [53] tandem deprotection/cycloaddition reaction conditions used to prepare 1,5-diaryl-1,2,3-triazole compounds. Identity of 1,5-diaryl-1,2,3-triazole control compounds prepared from tandem deprotection/click conditions (37

Synthesis of the tetracyclic skeleton of Aspidosperma alkaloids via PET-initiated cationic radical-derived interrupted [2 + 2]/retro-Mannich reaction

• Ru-Dong Liu,
• Jian-Yu Long,
• Zhi-Lin Song,
• Zhen Yang and
• Zhong-Chao Zhang

Beilstein J. Org. Chem. 2025, 21, 2470–2478, doi:10.3762/bjoc.21.189

• involves a formal 1,3-C shift. Keywords: Aspidosperma alkaloids; [2 + 2]-cycloaddition/retro-Mannich reaction; DFT study; photoinduced electron transfer; Introduction Photochemical reactions, which enable the construction of topologically complex architectures from simple building blocks, have attracted

• considerable attention in recent decades. Numerous approaches to natural product synthesis have been reported in which a photochemical transformation represents a key step [1][2][3]. In this context, the photochemical [2 + 2] cycloaddition and subsequent fragmentation of the resulting cyclobutane provides a

• leads to ketene D, which can undergo cycloaddition with an alkene to yield E. This fragmentation pathway dominates under various conditions (e.g., transition-metal catalysis, nucleophilic addition) and is driven by ring-strain release [11]. PET, an alternative to direct excitation and EnT, enables the

Transformation of the cyclohexane ring to the cyclopentane fragment of biologically active compounds

• Natalya Akhmetdinova,
• Ilgiz Biktagirov and
• Liliya Kh. Faizullina

Beilstein J. Org. Chem. 2025, 21, 2416–2446, doi:10.3762/bjoc.21.185

• aldehyde 53 [39] (Scheme 10). The key steps in this synthesis are based on an asymmetric rhodium-catalyzed [4 + 2] cycloaddition reaction [40], followed by a unique benzilic acid-type rearrangement under very mild conditions [41]. A step-by-step mechanism for the benzilic acid-type rearrangement of

The high potential of methyl laurate as a recyclable competitor to conventional toxic solvents in [3 + 2] cycloaddition reactions

• Ayhan Yıldırım and
• Mustafa Göker

Beilstein J. Org. Chem. 2025, 21, 2389–2415, doi:10.3762/bjoc.21.184

• against other solvents. Keywords: cycloaddition; fused isoxazolidines; renewable solvent; reusable solvent; trans-diastereoselectivity; Introduction It is an established fact that a significant number of conventional organic solvents, which are widely utilized in both industrial and academic contexts

• context of these strategies, it would be judicious to consider cycloaddition reactions of the [3 + 2] type, a field in which Smith and Huisgen are recognized as pioneers [24][25]. In the field of heterocyclic chemistry, the [3 + 2] type of cycloaddition reaction is a widely employed method for the

• consisting of a combination of isoxazolidine rings [36][37][38][39][40][41]. It has been demonstrated that such cycloaddition reactions are also employed in the efficient preparation of biologically active molecules, including nucleosides, β-lactam class antibiotics, peptides, and amino acids, as well as

Synthetic study toward vibralactone

• Liang Shi,
• Jiayi Song,
• Yiqing Li,
• Jia-Chen Li,
• Shuqi Li,
• Li Ren,
• Zhi-Yun Liu and
• Hong-Dong Hao

Beilstein J. Org. Chem. 2025, 21, 2376–2382, doi:10.3762/bjoc.21.182

• . This intermediate was intended to be prepared through allylation [36] with its precursor 15 accessible from aldehyde 16 and acetyl chloride through ketene–aldehyde [2 + 2] cycloaddition [37]. Results and Discussion Our synthetic route commenced from the known aldehyde 16 which is readily accessed in a

• single step from commercially available fructone [38] (Scheme 3). Following an efficient O-trimethylsilylquinine-catalyzed ketene–aldehyde cycloaddition and subsequent alkylation [36], 17 was synthesized. From 17, it was envisioned that the bicyclic skeleton could be efficiently constructed through ketal

Comparative analysis of complanadine A total syntheses

• Reem Al-Ahmad and
• Mingji Dai

Beilstein J. Org. Chem. 2025, 21, 2334–2344, doi:10.3762/bjoc.21.178

• intramolecular cyclization to afford alkyne–nitrile 19 for the first [2 + 2 + 2] cycloaddition with bis(trimethylsilyl)butadiyne (20). This transformation proceeded smoothly under thermal conditions with CpCo(CO)2 to afford 21 as the major regioisomer (rr = 25:1) [22]. Removal of the two TMS groups and

• reinstallation of a single TMS on the alkyne provided pyridyl-alkyne 22 for the second [2 + 2 + 2] cycloaddition reaction which proved nontrivial, with the protecting group on the secondary amine of the alkyne-nitrile moiety and the choice of ligand playing crucial roles. Specifically, when using 19 as the

• a thermal Diels–Alder cycloaddition, which afforded a mixture of stereo- (endo/exo) and regioisomers, among which the desired product 46 was obtained in 45% yield as a racemic mixture. After triflation of the free hydroxy group of 46 to provide 47, an intramolecular Heck reaction was employed to

Recent advances in Norrish–Yang cyclization and dicarbonyl photoredox reactions for natural product synthesis

• Peng-Xi Luo,
• Jin-Xuan Yang,
• Shao-Min Fu and
• Bo Liu

Beilstein J. Org. Chem. 2025, 21, 2315–2333, doi:10.3762/bjoc.21.177

• 56a (Scheme 9) – formed via [4 + 2] cycloaddition of singlet oxygen with the southern furan moiety in gracilisoid F (54) and gracilisoid H (56), respectively – served as branching points in the downstream divergent synthesis. Kornblum–DeLaMare-type rearrangement of 54a and 56a assembled gracilisoids B

• -obscurine (83) as a late-stage common intermediate. Compound 83 was readily accessible via previously reported protocols [40], which featured a diastereoselective formal [3 + 3] cycloaddition between 76 and 81 as the key step. This cycloaddition constructs the three contiguous stereocenters and two C–C

• protection as ketal and nitrile reduction. The two building blocks (76 and 81) were then merged through the desired formal [3 + 3]-cycloaddition to generate N-desmethyl-α-obscurine (82), presumably via in situ-generated intermediates 76a and 81a, respectively. Subsequent Boc protection of the cyclic amine in

Enantioselective radical chemistry: a bright future ahead

• Anna C. Renner,
• Sagar S. Thorat,
• Hariharaputhiran Subramanian and
• Mukund P. Sibi

Beilstein J. Org. Chem. 2025, 21, 2283–2296, doi:10.3762/bjoc.21.174

• transformations [43][44][45][46][47][48]. Using SOMO catalysis, MacMillan and co-workers developed a method for the synthesis of substituted pyrrolidines from β-aminoaldehydes and olefins in a formal [3 + 2] cycloaddition (Scheme 2) [44]. The transformation was proposed to proceed via a radical–polar crossover

Pathway economy in cyclization of 1,n-enynes

• Hezhen Han,
• Wenjie Mao,
• Bin Lin,
• Maosheng Cheng,
• Lu Yang and
• Yongxiang Liu

Beilstein J. Org. Chem. 2025, 21, 2260–2282, doi:10.3762/bjoc.21.173

• distinct from those generated through thermal Diels–Alder cycloaddition of (Z)-100. However, when [ReCl(CO)5] was used as the catalyst, a regioselective C–H bond insertion pathway was observed for substrate (E)-100, leading to the formation of tricyclic products 104 and 105 (Scheme 21, path b). This

• controlled synthesis of nitrogen-containing heterocycles via reaction pathway modulation (Scheme 32) [45]. Under catalysis of Cu(OAc)2 and HOAc, the substrate was subjected to decyanation and followed copper-promoted [2 + 2] cycloaddition that yielded cyclobutene intermediate 155. Carbocation rearrangement

• 60 °C initiated nickel-mediated intramolecular [2 + 2] cycloaddition to form dihydrocyclobuta[c]quinolin-3-one framework 164. Conversely, when the temperature was elevated to 140 °C, thermal ring-expansion of the four-membered intermediate was induced through C–C bond cleavage/reorganization

Synthesis of triazolo- and tetrazolo-fused 1,4-benzodiazepines via one-pot Ugi–azide and Cu-free click reactions

• Xiaoming Ma,
• Zijie Gao,
• Jiawei Niu,
• Wentao Shao,
• Shenghu Yan,
• Sai Zhang and
• Wei Zhang

Beilstein J. Org. Chem. 2025, 21, 2202–2210, doi:10.3762/bjoc.21.167

• /bjoc.21.167 Abstract A one-pot Ugi–azide reaction followed by intramolecular Cu-free azide–alkyne cycloaddition generates a polycyclic scaffold 7 bearing polycyclic triazole, tetrazole, and benzodiazepine rings. This method could be extended for obtaining a more complicated scaffold 8 containing a

• ]. We herein propose a one-pot synthesis involving an Ugi–azide 4-component (4-CR) reaction followed by lactamization and azide–alkyne cycloaddition for assembling triazole-fused and tetrazole-tethered 1,4-benzodiazepines 7 and triazole-, tetrazole-, and piperazinone-fused 1,4-benzodiazepines 8 (Scheme

• advantages over traditional copper-catalyzed azide–alkyne cycloaddition (CuAAC) reactions, including operational simplicity and the absence of metal contaminants, which is crucial for pharmaceutical applications. After having identified suitable reaction conditions of the Ugi–azide and click reactions for

Electrochemical cyclization of alkynes to construct five-membered nitrogen-heterocyclic rings

• Lifen Peng,
• Ting Wang,
• Zhiwen Yuan,
• Bin Li,
• Zilong Tang,
• Xirong Liu,
• Hui Li,
• Guofang Jiang,
• Chunling Zeng,
• Henry N. C. Wong and
• Xiao-Shui Peng

Beilstein J. Org. Chem. 2025, 21, 2173–2201, doi:10.3762/bjoc.21.166

• alkynes, amines and azides, respectively. Imidazopyridines could be obtained by electrochemical [3 + 2] cyclization of heteroarylamines. The electrochemical oxidative [3 + 2] cycloaddition of secondary propargyl alcohols was a simple and efficient access towards 1,2,3-triazoles. In this review

• [61], [3 + 2] reductive cycloadditions of enal-alkyne [62], [2 + 2 + 1] cycloaddition of acetylenes [63] and cyclization of 1,6-enyne [64] were efficient approaches towards five-membered rings. Since Faraday synthesized hydrocarbons by employing electric current to an acetate solution [65], the use of

• of carbamates as well [271]. Notably, the above approach provided imidazopyridines in high yields under aqueous solution without any metal catalysts. Early in 2008, an electrochemical copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) to access 1,2,3-triazole was realized by Finn [272]. But the

C2 to C6 biobased carbonyl platforms for fine chemistry

• Jingjing Jiang,
• Muhammad Noman Haider Tariq,
• Florence Popowycz,
• Yanlong Gu and
• Yves Queneau

Beilstein J. Org. Chem. 2025, 21, 2103–2172, doi:10.3762/bjoc.21.165

• Griesbeck reported the tetraphenylporphin-photosensitized oxygenations of furan and derivatives in non-polar aprotic solvents, yielding the corresponding monomeric unsaturated secondary ozonides through a (4 + 2) cycloaddition of singlet oxygen onto the diene linkage of the furan ring. The attack of a

• . Then, through acetylation and subsequent base-mediated oxidopyrylium [5 + 2] cycloaddition reactions, 1-(trifluoromethyl)-8-oxabicyclo[3.2.1]oct-3-en-2-ones were prepared (Scheme 58) [190]. Chu and Webster reported the photocatalyzed synthesis of furfural-derived diacids from furfural [191][192

The application of desymmetric enantioselective reduction of cyclic 1,3-dicarbonyl compounds in the total synthesis of terpenoid and alkaloid natural products

• Dong-Xing Tan and
• Fu-She Han

Beilstein J. Org. Chem. 2025, 21, 2085–2102, doi:10.3762/bjoc.21.164

• operation including azide–alkene dipolar cycloaddition, irradiation of the resulting triazoline to aziridine 80 and in situ ring opening followed by deacetylation achieved the first total synthesis of (−)-hunterine A (14). On the other hand, aza-Cope/Mannich reaction of 78 produced imine intermediate 81

• insertion [74] with ketone 91 and deprotection of the dithiane group delivered alleneketone 92. Sequential treatment of 92 with TsNHNH2 and NaH, the trimethylenemethane (TMM) diyl-mediated cycloaddition via intermediates 93 and 94 proceeded uneventfully to form the tetracyclic product 95. Next, reductive

Bioinspired total syntheses of natural products: a personal adventure

• Zhengyi Qin,
• Yuting Yang,
• Nuran Yan,
• Xinyu Liang,
• Zhiyu Zhang,
• Yaxuan Duan,
• Huilin Li and
• Xuegong She

Beilstein J. Org. Chem. 2025, 21, 2048–2061, doi:10.3762/bjoc.21.160

• reported. A bioinspired approach represents many advantages to bring benefits to total synthesis. It could rapidly achieve complexity of the target molecule from a much simpler precursor in diverse forms of transformations such as cascade reaction, cycloaddition, and C–H functionalization, thereby, shorten

• -phellandrene provided a steric effect to the cycloaddition. Then, sarglamides D and E arose from C through acid-promoted oxy-cyclizations. This biosynthetic approach rapidly constructs the complex structure from simple precursors, thus we intended to achieve the total synthesis of sarglamides through the

α-Ketoglutaric acid in Ugi reactions and Ugi/aza-Wittig tandem reactions

• Vladyslav O. Honcharov,
• Yana I. Sakhno,
• Olena H. Shvets,
• Vyacheslav E. Saraev,
• Svitlana V. Shishkina,
• Tetyana V. Shcherbakova and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2025, 21, 2021–2029, doi:10.3762/bjoc.21.157

• for the preparation of benzodiazepinone derivatives, which showed promising psychotropic effects [20][21][22][23][24], using a tandem combination of Ugi/azide–alkyne cycloaddition reactions. From this point of view, azido amines are promising reagents for use in the Ugi reaction, opening up the

Understanding the origin of stereoselectivity in the photochemical denitrogenation of 2,3-diazabicyclo[2.2.1]heptene and its derivatives with non-adiabatic molecular dynamics

• Leticia A. Gomes and
• Steven A. Lopez

Beilstein J. Org. Chem. 2025, 21, 2007–2020, doi:10.3762/bjoc.21.156

• starting materials for different types of reactions including thermal isomerization to cyclopentenes [36][37][38] and 1,4-pentadienes [37][38], chemical electron-transfer oxidations to cyclopentene [39] and cycloaddition reactions with electron-deficient alkenes and alkynes [38][40][41] (Scheme 1b

Enantioselective desymmetrization strategy of prochiral 1,3-diols in natural product synthesis

• Lihua Wei,
• Rui Yang,
• Zhifeng Shi and
• Zhiqiang Ma

Beilstein J. Org. Chem. 2025, 21, 1932–1963, doi:10.3762/bjoc.21.151

• transformation involving acyl-group migration, [4 + 2] cycloaddition and aromatic Pummerer-type reaction, provided chiral spiro compound 59 with the 6/6/5/5/6/6 scaffold, and this intermediate was further elaborated to 60 in six additional steps. Lipases from Pseudomonas genus Pseudomonas is a genus of Gram

• hetisine-type diterpenoids (+)-18-benzoyldavisinol and (+)-davisinol [82] (Scheme 34). Using diester 286 as a starting material, phenol 287 was prepared in six steps. Subsequent oxidative dearomatization-induced Diels–Alder cycloaddition with PhI(OAc)2, delivered endo-cycloadduct 288 with high

Preparation of spirocyclic oxindoles by cyclisation of an oxime to a nitrone and dipolar cycloaddition

• Beth L. Ritchie,
• Alexandra Longcake and
• Iain Coldham

Beilstein J. Org. Chem. 2025, 21, 1890–1896, doi:10.3762/bjoc.21.146

• an important class of compounds with significant biological activities. Spirocyclic derivatives are present in a variety of natural products. We describe here the formation of spirooxindoles using an intermolecular nitrone cycloaddition reaction. The nitrone dipole was prepared in situ by cyclisation

• condensation, cyclisation, and cycloaddition as an efficient strategy for the rapid formation of complex spirocyclic products that could have value for the formation of novel, bioactive oxindoles. Keywords: cascade; cycloaddition; oxindole; spirocycle; stereochemistry; Introduction The Alstonia alkaloids are

• -containing compounds makes use of intramolecular 1,3-dipolar cycloaddition reactions [15], including examples with nitrone ylides [16][17][18][19][20][21][22]. Our research group has exploited this approach for the synthesis of alkaloids such as myrioxazine A and aspidospermidine [23][24]. With a nitrone 1,3

Chiral phosphoric acid-catalyzed asymmetric synthesis of helically chiral, planarly chiral and inherently chiral molecules

• Wei Liu and
• Xiaoyu Yang

Beilstein J. Org. Chem. 2025, 21, 1864–1889, doi:10.3762/bjoc.21.145

• , including the asymmetric [2 + 2 + 2] cycloaddition of aryl-substituted polyynes and hydroarylation of alkynes [18][19]. In contrast, the application of asymmetric organocatalysis for enantioselective synthesis of chiral helicenes remains relatively underdeveloped compared to transition metal-catalyzed

• eliminative aromatization sequence [23]. The CPA-catalyzed asymmetric [3 + 2]-cycloaddition of cycloenecarbamates 21 and carbalkoxy-substituted azonaphthalenes 22 produced the hexacyclic products 23' with two contiguous stereogenic centers, which then underwent an eliminative aromatization process to yield

• through a [3 + 3]-cycloaddition reaction. By employing the CPA-catalyzed asymmetric electrophilic amination reaction with azodicarboxylate on the phenol moiety, efficient kinetic resolution of 25 proceeded to yield both the amination products 26 and the recovered starting material with high

Fe-catalyzed efficient synthesis of 2,4- and 4-substituted quinolines via C(sp²)–C(sp²) bond scission of styrenes

• Prafull A. Jagtap,
• Manish M. Petkar,
• Vaishnavi R. Sawant and
• Bhalchandra M. Bhanage

Beilstein J. Org. Chem. 2025, 21, 1799–1807, doi:10.3762/bjoc.21.142

• cycloaddition, tandem annulation, intramolecular cyclization, and cross-coupling reactions are commonly employed under thermal conditions, utilizing metal catalysts based on Pd, Ru, Au, Cu, and Fe to access a wide array of substituted quinoline frameworks [29][30][31][32][33][34][35][36][37][38]. Conversely, in

• the FeIII species. An alternative mechanism involving a concerted [4 + 2] cycloaddition between the aza-butadiene moiety in II and the alkene, leading to intermediate IV, cannot be ruled out. Conclusion In summary, we have successfully developed a highly efficient method for the oxidative C–C bond

[3 + 2] Cycloaddition of thioformylium methylide with various arylidene-azolones in the synthesis of 7-thia-3-azaspiro[4.4]nonan-4-ones

• Daniil I. Rudik,
• Irina V. Tiushina,
• Anatoly I. Sokolov,
• Alexander Yu. Smirnov,
• Alexander R. Romanenko,
• Alexander A. Korlyukov,
• Andrey A. Mikhaylov and
• Mikhail S. Baranov

Beilstein J. Org. Chem. 2025, 21, 1791–1798, doi:10.3762/bjoc.21.141

• single either cis or trans stereoisomers, dependent on the heterocycle core used. Keywords: arylidene-azolones; cycloaddition; nitrogen heterocycles; sulfur heterocycles; thioformylium methylide; Introduction Spirocyclic derivatives of heterocycles occupy an important place in modern organic and

• -membered heterocyclic ring are of particular interest, since they exhibit a wide range of pharmacological activity (Scheme 1) [6][7][8][9][10][11]. The most straightforward and powerful methods of such substance’s syntheses are based on cycloaddition reactions [12][13][14][15]. Previously, we and other

• tetrahydrothiophenes are known to exhibit different biological activities [8]. However, to date the use of this reagent in the synthesis of spirocyclic derivatives to our knowledge is underinvestigated [26][27]. Results and Discussion In this work we present a systematic study of [3 + 2] cycloaddition of thioformylium