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

Regioselective cobalt(II)-catalyzed [2 + 3] cycloaddition reaction of fluoroalkylated alkynes with 2-formylphenylboronic acids: easy access to 2-fluoroalkylated indenols

• Tatsuya Kumon,
• Miroku Shimada,
• Jianyan Wu,
• Shigeyuki Yamada and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 2193–2200, doi:10.3762/bjoc.16.184

• [2 + 3] cycloaddition reactions with a broader substrate scope for the synthesis of fluoroalkylated indenols is still required. Herein we present a synthesis of 2-fluoroalkylated indenols via [2 + 3] cycloadditions of various fluorinated alkynes with 2-formylphenylboronic acids in the presence of

A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

• Olusesan K. Koleoso,
• Matthew Turner,
• Felix Plasser and
• Marc C. Kimber

Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165

• innovative transformations, including cycloadditions [5][6][7][8][9], intramolecular cyclizations and intermolecular addition reactions [10][11][12][13][14][15][16][17][18], as well as the use of the allenamide building block in natural product synthesis [1]. Addition reactions of allenamides, which can also

Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

• Dominik Göbel,
• Marius Friedrich,
• Enno Lork and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

• cycloadditions with model alkynes. Besides two ortho- and para-bromo-substituted benzaldehydes, the azide functionalization of a fluorene-based structure will be presented. The copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of the so-synthesized azide-functionalized bromocarbaldehydes with terminal

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

• -substituted β-lactone products in a high yield, diastereo-, and enantioselectivity (Figure 2A) [46]. Chi and co-workers have reported limited examples of oxidative [2 + 2] cycloadditions using hydrocinnamaldehyde as an azolium enolate precursor and the NHC precatalyst 2, giving β-lactone products in high

• [54]. We have previously applied these precursors in the NHC-catalyzed formal [2 + 2] cycloadditions between α-aroyloxyaldehydes and perfluoroalkyl-substituted ketones using NHC precatalyst 3 to produce polyfluorinated oxetanes and β-perfluoroalkyl-β-hydroxyamides after derivatization [55]. In this

• -hydroxyamide (Scheme 3). Conclusion In this paper, we showed that azolium enolates generated from α-aroyloxyaldehydes can undergo NHC-catalyzed formal [2 + 2] cycloadditions with trifluoroacetophenone derivatives. Although the β-lactone products proved unstable to chromatographic purification, ring opening

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• cyclization, and an elimination give the desired product 27 (Scheme 7). The use of PhSSPh obviated the undesired reactions, which occurred when using Ph3SnH and Bu3SnH, respectively, as the catalyst for this reaction. Oxidation reactions Not only can disulfide catalysts induce cycloadditions of olefins but

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• + 2] cycloadditions, ring expansions and contractions, nucleophilic cyclizations, and some miscellaneous methods. The recently developed methods provide some new strategies for the efficient preparation of thietanes and their derivatives. This review focuses on the synthetic methods to construct

• , or disulfonates of alkane-1,3-diols with sodium sulfide. The intramolecular substitution of 3-mercaptoalkyl halides or sulfonates is a similar strategy for the preparation of thietanes [12][13][14]. Alternatively, inter- and intramolecular photochemical [2 + 2] cycloadditions (thia-Paternò–Büchi

• reactions) of alkenes and thiocarbonyl compounds are another important route for the synthesis of thietanes [15][16], especially, spirothietanes [17][18]. The formal [2 + 2] cycloadditions of hexafluorothioacetone and olefins are also applied in the preparation of bis(trifluoromethyl)-containing thietanes

Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole

• Carlos H. Escalante,
• Eder I. Martínez-Mora,
• Carlos Espinoza-Hicks,
• Alejandro A. Camacho-Dávila,
• Fernando R. Ramos-Morales,
• Francisco Delgado and
• Joaquín Tamariz

Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113

• diffraction crystallography of both endo 9m and exo 10m adducts (Figure 2) [43]. In addition, the thermal cycloadditions of 2-vinylpyrroles 8a–j and maleimides 7b,c took place satisfactorily to deliver the expected adducts 9e–p/10e–p, also with high endo diastereoselectivity and good yields (Table 2, entries

• 5–16). None of the series of mixtures 9a–p/10a–p corresponds to the direct products of the Diels–Alder cycloadditions, since they are derivatives resulting from the double bond isomerization of adducts 17 (i.e., migration from the pyrrole-fused exo cyclic position to the endo cyclic aromatic

• (Scheme 6). Although the reactivity was much lower (10 days) compared to the cycloadditions with 2-vinylpyrroles 8a–h (7 days) (Table 2), the diastereoselectivity remained rather high and similar to derivatives 8g and 8h. Considering the significant biological activity of indoles, octahydropyrrolo[3,4-e

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

• Margareta Sohora,
• Leo Mandić and
• Nikola Basarić

Beilstein J. Org. Chem. 2020, 16, 1296–1304, doi:10.3762/bjoc.16.110

• systems for the control of photoreactivity. Keywords: [3 + 2] cycloadditions; β-cyclodextrin; inclusion complexes; photochemistry; phthalimides; Introduction Cycloadditions are highly useful reactions in organic synthesis providing complex cyclic structures from easily available precursors [1][2]. Among

• different reactions, [3 + 2] cycloadditions showed applicability in the synthesis of heterocyclic 5-ring compounds [3], as well as in the green synthesis of a number of natural products [4]. One of the useful synthons in [3 + 2] cycloadditions is azomethine ylide [5][6][7], also used in intramolecular

• complex molecules and natural products [11] since the pioneering work of Kanaoka et al. [12]. Photochemical reactions of phthalimides include H-abstractions, cycloadditions and photoinduced electron transfer (PET)[13]. We became interested in the application of photochemical H-abstraction reactions

Ferrocenyl-substituted tetrahydrothiophenes via formal [3 + 2]-cycloaddition reactions of ferrocenyl thioketones with donor–acceptor cyclopropanes

• Grzegorz Mlostoń,
• Mateusz Kowalczyk,
• André U. Augustin,
• Peter G. Jones and
• Daniel B. Werz

Beilstein J. Org. Chem. 2020, 16, 1288–1295, doi:10.3762/bjoc.16.109

• practical importance [1][2]. The development of chemo- and diastereoselective syntheses for these compounds is thus a challenging problem. An elegant and highly efficient method for the construction of the tetrahydrothiophene ring is based on 1,3-dipolar cycloadditions of in-situ-generated thiocarbonyl S

• by means of spectroscopic methods (R = CF3). In a recent work, an alternative, efficient and useful method for the synthesis of highly functionalized tetrahydrothiophenes of type 6 was reported [9] (Scheme 2). Under Lewis acid catalysis, formal [3 + 2]-cycloadditions of aromatic and cycloaliphatic

• the formal [4 + 3]-cycloaddition [10] (Scheme 2). In a series of our recent publications, ferrocenyl/aryl and ferrocenyl/alkyl thioketones were demonstrated to be attractive substrates for the preparation of six- and five-membered sulfur heterocycles via [4 + 2]- and [3 + 2]-cycloadditions

Synthesis of pyrrolidinedione-fused hexahydropyrrolo[2,1-a]isoquinolines via three-component [3 + 2] cycloaddition followed by one-pot N-allylation and intramolecular Heck reactions

• Xiaoming Ma,
• Suzhi Meng,
• Xiaofeng Zhang,
• Qiang Zhang,
• Shenghu Yan,
• Yue Zhang and
• Wei Zhang

Beilstein J. Org. Chem. 2020, 16, 1225–1233, doi:10.3762/bjoc.16.106

• related to natural products [18][19][20]. Among the well-established MCRs, three-component 1,3-dipolar cycloadditions of benzaldehydes, maleimides, and amino esters have been developed for making N-containing 5-membered heterocycles (Scheme 1) [21][22]. The [3 + 2] cycloadditions of maleimides with

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• a suitable Michael acceptor 24.2 to obtain the corresponding allylation product 24.3 after a desulfonylation. Enones can also be subject to SET reductions through photoredox catalysis, and this can lead to [2 + 2] cycloadditions [2][108]. Similar intermediates can also be generated through the

Copper-catalysed alkylation of heterocyclic acceptors with organometallic reagents

• Yafei Guo and
• Syuzanna R. Harutyunyan

Beilstein J. Org. Chem. 2020, 16, 1006–1021, doi:10.3762/bjoc.16.90

• functionalised alkyl chains at the β-position of the alkenylpyridines, the catalytic system also showed a high functional group tolerance, and thus allowing straightforward chemical transformations of the addition products, including, for example, reductions, cycloadditions, and coupling reactions (Scheme 15B

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• acids using Pt or Pd porphyrins. Photocatalytic reduction of various nitroaromatics using a Ni-MOF. Photoinduced cycloadditions of CO2 with epoxides by MOF1. TPP-photocatalyzed generation of 1O2 and its application in organic synthesis. Adapted from [67][68][69]. Pericyclic reactions involving singlet

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• K562 cells [87][88]. In this innovative work, the authors effectively combined an enyne metathesis promoted by the Grubbs first-generation catalyst and an alkene cross-metathesis induced by the Grubbs second-generation catalyst with reverse electron-demand Diels–Alder cycloadditions (Scheme 20). In

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• protecting groups [12]. Later, ruthenium complexes-catalyzed alkyne–azide cycloadditions (RuAACs) regioselectively produced the opposite form of the disubstituted triazoles. Thus, a wide range of azides was reacted with diverse nonactivated terminal alkyne substrates using ruthenium complexes to generate

• 100 °C for one day, cooled, and filtered. The material Pd–Cu@rGO (78), as heterogeneous nanocatalyst, was prepared by anchoring Pd(OAc)2 on Cu@rGO in toluene via pyrolysis. The catalyst was highly active in one-pot condensations of alkyl/aryl-substituted triazole heterocycles with cycloadditions and

• , copper nanoparticles-decorated three-dimensional graphene (3D graphene/Cu nanocomposite 87) was reported as a catalyst to perform Huisgen 1,3‐dipolar cycloadditions. Therein, the GO material was mixed with EDA to produce a stable suspension that was transferred to a teflon‐lined autoclave. After heating

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• ; chemoinformatics; Cu-catalysis; cycloadditions; molecular scaffolds; multicomponent reactions; Introduction The screening of small molecule libraries is a well-established approach in early-stage drug discovery to identify hit candidates for the development of drug leads. The application of unconventional

Synthetic terpenoids in the world of fragrances: Iso E Super^® is the showcase

• Alexey Stepanyuk and
• Andreas Kirschning

Beilstein J. Org. Chem. 2019, 15, 2590–2602, doi:10.3762/bjoc.15.252

• ]. Following this invention, many derivatives were produced to find new viable targets. These studies mostly focused on Diels–Alder cycloadditions to create structures that resemble terpenoids readily available from easily accessible and affordable starting materials like myrcene (1). One of the newly found

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• . Tables providing comprehensive directories of fulvene cycloaddition chemistry are provided, including fulvene intramolecular and intermolecular cycloadditions complete with reactant partners and their resulting cyclic adducts, which provide a useful reference source for synthetic chemists working with

• , this can result in a bathochromic shift [2][42]. Consideration of frontier molecular orbital theory allows the electronic nature and general reactivity patterns of fulvenes to be interpreted. Fulvene cycloadditions The multiple cycloaddition pathways observed for fulvenes provides access to a diverse

• fulvene to function as a 6π component in reactions with electron-deficient dienes (Scheme 5b) and fulvenes acting as dipolarophiles have been reported for enantioselective [6 + 3] and [3 + 2] cycloadditions [83][84][105]. In general, reactions with electron-rich alkenes will take place preferentially at

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• electrophilicity made lanthanides a catalyst of choice. Lanthanum complexes are widely used in synthetic chemistry for cycloadditions, reductions, benzimidazole syntheses, Biginelli reactions, hydrophosphinations of unsaturated substrates, double hydrophosphinylations of unactivated nitriles, Grignard additions, C

Transient and intermediate carbocations in ruthenium tetroxide oxidation of saturated rings

• Manuel Pedrón,
• Laura Legnani,
• Maria-Assunta Chiacchio,
• Pierluigi Caramella,
• Tomás Tejero and
• Pedro Merino

Beilstein J. Org. Chem. 2019, 15, 1552–1562, doi:10.3762/bjoc.15.158

• transient carbocations in reactions taking place in one kinetic step including asynchronous concerted cycloadditions [36] and SN2-type reactions [37]. Moreover, the real existence of transient carbocations – which are not energy minima – predicted computationally has also been recently proven experimentally

Diaminoterephthalate–α-lipoic acid conjugates with fluorinated residues

• Leon Buschbeck,
• Aleksandra Markovic,
• Gunther Wittstock and
• Jens Christoffers

Beilstein J. Org. Chem. 2019, 15, 981–991, doi:10.3762/bjoc.15.96

• example for an application in biochemistry, Figure 1 shows a compound with cyclooctyne and maleimide as functional units. It was used as a "turn-on" fluorescence probe for cross-linking proteins [13]. The highly reactive cyclooctyne residue undergoes 1,3-dipolar cycloadditions with organoazides (copper

Solid-phase synthesis of biaryl bicyclic peptides containing a 3-aryltyrosine or a 4-arylphenylalanine moiety

• Iteng Ng-Choi,
• Àngel Oliveras,
• Lidia Feliu and
• Marta Planas

Beilstein J. Org. Chem. 2019, 15, 761–768, doi:10.3762/bjoc.15.72

• -terminal groups of the peptide and their putative target. This method has been used for the macrocyclization of peptides through, for example, copper-catalyzed azide–alkyne cycloadditions [14], ring-closing olefin metathesis [13] or the formation of an aryl–aryl bond between the side chain of two aromatic

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Katarzyna Urbaniak,
• Marcin Jasiński,
• Vladyslav Bakhonsky,
• Peter R. Schreiner and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43

• reactivity analogous to aldonitrones, which enables their conversion via [3 + 2]-cycloadditions with dipolarophiles such as activated ethylenes [8][9], activated acetylenes [10][11] or isocyanates [11][12]. The initially formed [3 + 2]-cycloadducts undergo spontaneous secondary conversions leading to re

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

• Andrejs Šišuļins,
• Jonas Bucevičius,
• Yu-Ting Tseng,
• Irina Novosjolova,
• Kaspars Traskovskis,
• Ērika Bizdēna,
• Huan-Tsung Chang,
• Sigitas Tumkevičius and
• Māris Turks

Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41

• cycloadditions varied from 51% to 76% in the case of pyrrolidinyl purines 7a–f and from 53% to 86% for piperidinyl purines 8a–f (Table 1 and Table 2). To gain an insight into the structure–photophysical properties relationship of the newly obtained structures, various EDG and EWG at the para-position of the