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

• thioketones 8 in the presence of a Lewis acid was based on the assumption that the coordination of the catalyst by two ester groups activated the cyclopropane ring and allowed a nucleophilic attack of the C=S group on the benzylic position of the cyclopropane derivative (Scheme 4). The subsequent ring-closure

• involved the formation of the reactive, zwitterionic intermediate 10. It seemed that repulsive interactions of the aryl groups Ar (from cyclopropane 5) and R (from thioketone 8) controlled the diastereoselective ring-closure to the five-membered ring leading in these cases to the formation of cis-9 (Ar to

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

• system to perform a ring closure/pyridylation radical cascade for the synthesis of tetrahydrofuran derivatives (Scheme 39b) [161]. Eosin Y (OD13) has been demonstrated to be another competent photocatalyst for the generation of O-centered radicals from N-alkoxypyridynium salts. These radicals have been

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• a certain extent Hg2+) initially induced a ring-opening reaction that was irreversibly followed by a fast ring closure–deprotonation–oxidation sequence to give styryl-substituted naphthoxazole derivatives as the products quantitatively. For the quinolizinium-substituted spirooxazine derivative, the

• short-lived absorption band between 500 and 650 nm, which supports this hypothesis and suggests that the processes have different rate constants in the presence of Cu2+ or Fe3+. We finally propose that the following reaction steps, i.e., the ring closure, deprotonation, and electron transfer to a second

Copper catalysis with redox-active ligands

• Agnideep Das,
• Yufeng Ren,
• Cheriehan Hessin and
• Marine Desage-El Murr

Beilstein J. Org. Chem. 2020, 16, 858–870, doi:10.3762/bjoc.16.77

• in equilibrium with a spectator bis-nitrene species 19 and proceeded through styrene 20 insertion, followed by ring closure and release of the aziridine. Interestingly, this otherwise classical mechanism is enabled by the accessibility of doublet and quadruplet states close in energy and this

• reminiscent of the entatic state model. The proposed mechanism (Scheme 12) involves the insertion of a nitrene or carbene group to the copper complex 22 to form intermediate 23. Subsequent alkene insertion yields species 25 and the group-transfer product (21a,h–j,n,o, 26a–g and 27a–o) is released upon ring

• -closure (Scheme 12). A wide range of substrates including diverse mono-, di-, and trisubstituted styrene derivatives (21a,i,h, 26a–d and 27a–i) substrates as well as unactivated or deactivated tri- and tetrasubstituted scaffolds (21j,n,o, 26e–g and 27j–o) were efficiently converted. Conclusion The use of

Synthesis of disparlure and monachalure enantiomers from 2,3-butanediacetals

• Adam Drop,
• Hubert Wojtasek and
• Bożena Frąckowiak-Wojtasek

Beilstein J. Org. Chem. 2020, 16, 616–620, doi:10.3762/bjoc.16.57

• , giving compounds 22 and 23. The butanediacetal groups were then removed with p-toluenesulfonic acid and diols 5 and 6 were obtained with 79% and 64% yield, respectively. They were then used in a well-established three-step, one-pot procedure for epoxide ring closure [26][30][40][41]. Pure (+)-disparlure

Synthesis of triphenylene-fused phosphole oxides via C–H functionalizations

• Md. Shafiqur Rahman and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2020, 16, 524–529, doi:10.3762/bjoc.16.48

• catalyst (Scheme 2). This one-pot construction of the benzo[b]phosphole core ensured the preferential phosphole ring closure in proximity of the alkoxy group of the arylzinc reagent 1 (regioselectivity of ≈3:1), presumably due to a secondary interaction between the MOM group and the cobalt catalyst during

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• unlikely to compete with ring closure to F for entropic reasons. All attempts to trap intermediate C using methanol or acetic acid as co-solvent (see Table 2) were unsuccessful and resulted in lower yields, especially in the case of methanol, likely due to the increased polarity of the reaction mixture

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• different ratios governed by the phosphine substituents (Scheme 13) [75]. When the R-substituent is more electron donating, the pyridine nitrogen ortho to the phosphine becomes more nucleophilic and intermediate 70 undergoes ring closure to give compound 71 with the phosphanyl substitutent in the 7-position

Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)

• Ryo Takishima,
• Yuji Nishii,
• Tomoaki Hinoue,
• Yoshitane Imai and
• Masahiro Miura

Beilstein J. Org. Chem. 2020, 16, 325–336, doi:10.3762/bjoc.16.32

• available (S)- and (R)-1,1’-bi-2-naphthols through a palladium-catalyzed multiple intramolecular C–H/C–H coupling as the key ring-closure step. The effect of terminal tert-butyl substituents on the BBZFPy skeleton was systematically investigated to uncover a unique aggregation-induced enhancement of CPL

Microwave-assisted synthesis of 2-substituted 4,5,6,7-tetrahydro-1,3-thiazepines from 4-aminobutanol

• María C. Mollo,
• Natalia B. Kilimciler,
• Juan A. Bisceglia and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2020, 16, 32–38, doi:10.3762/bjoc.16.5

• -substituted tetrahydro-1,3-thiazepines by MW-assisted cyclization of 4-thioamidobutanols is presented. The acyclic precursors were prepared in high overall yields by an expeditious three-step diacylation/thionation/deprotection sequence from 4-aminobutanol. Microwave-assisted ring closure of 4-thioamido

• ]. On the other hand, the seven-membered iminothioethers (4,5,6,7-tetrahydro-1,3-thiazepines) have remained almost unexplored. This virtual void is probably due to the known difficulty of the annulation of seven-membered heterocyclic rings. In fact, ring closure reactions leading to medium-sized

• solvents [43]. Ring closure reactions leading to different heterocyclic cores are relevant among the synthetic applications of PPA esters. The use of MW irradiation as the energy source in these reactions [44][45][46][47] is of particular interest due to the many advantages associated with MAOS: very short

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• (Figure 1) [25][27]. Switching of such diarylethene dyes in both directions (ring closure/coloration or ring opening/discoloration) by UCNPs has been documented for years, with a seminal work reported in 2009 by the team of Branda [28]. In the following we will show how this photochromic compound can be

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1’-diacetylenic ferrocenes

• Celine Bittner,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2019, 15, 2534–2543, doi:10.3762/bjoc.15.246

• same direction and as a result of the larger ring size the alkyne moiety is laying almost in the plane of Ct11. The dimeric compound unfortunately could not be crystallised from the mixture with 2b. Interestingly, in the case of the butynyl substrate 1a exclusively the monomeric ring closure to

• . In the following catalytic conversion, no ring closure could be observed as the proton NMR spectrum showed the starting material exclusively with the characteristic signals for the terminal proton of the C≡CH triple bond at 2.52 ppm. However, this behaviour is in good agreement with other literature

Current understanding and biotechnological application of the bacterial diterpene synthase CotB2

• Ronja Driller,
• Daniel Garbe,
• Norbert Mehlmer,
• Monika Fuchs,
• Keren Raz,
• Dan Thomas Major,
• Thomas Brück and
• Bernhard Loll

Beilstein J. Org. Chem. 2019, 15, 2355–2368, doi:10.3762/bjoc.15.228

• deuterium labeling [33][34][35], to form the carbocation located at position C8 of dolabellatrienyl (B). By ring closure and formation of a novel C–C bond the tricyclic 5–8–5 ring system (C) is established. F107, F149, and the pyrophosphate moiety stabilize the carbocation at position C3 (Scheme 2 and

Mono- and bithiophene-substituted diarylethene photoswitches with emissive open or closed forms

• A. Lennart Schleper,
• Mariano L. Bossi,
• Vladimir N. Belov and
• Stefan W. Hell

Beilstein J. Org. Chem. 2019, 15, 2344–2354, doi:10.3762/bjoc.15.227

• open forms with rather low emission efficiency. The photoswitching kinetics was studied at several wavelengths with UV and visible light. New diarylethenes underwent ring-closure reactions by irradiation with UV light (365 nm, 405 nm), and the reversible ring-opening by irradiation with visible light

• (470 nm, 530 nm). The on-switching of fluorescence due to the ring-closure reaction was observed also with visible light of 470 nm (to an extent of 10% for compound SyOTh1) and attributed to the Urbach tail effect. Due to a high degree of fluorescence modulation (>270), good fatigue resistance and

• ring-closure reaction was fully reversible by irradiation with longer wavelengths. This offers the possibility of reversible switching a DAE only with visible, avoiding harmful (cytotoxic) UV irradiation. In view of the forthcoming solubilizing strategies applicable to fluorescent DAEs and intended for

Harnessing enzyme plasticity for the synthesis of oxygenated sesquiterpenoids

• Melodi Demiray,
• David J. Miller and
• Rudolf K. Allemann

Beilstein J. Org. Chem. 2019, 15, 2184–2190, doi:10.3762/bjoc.15.215

• closure to form the bisabolyl cation (6). A [1,3]-hydride shift to form carbocation 7 and 1,10-ring closure yield the amorphyl cation (8). Finally, deprotonation generates amorpha-4,11-diene (3) [8][9]. Several sesquiterpene synthases including ADS accept FDP analogues containing a variety of heteroatoms

• ]. Mechanistically, isomerisation of 12 to the methoxy-NDP analogue 28 allows for an ADS-catalysed 1,6-cyclisation to the 12-methoxy-bisabolyl cation (29) followed by a [1,3]-hydride shift, which relocates the positive charge on C1 in 30. With FDP and 12-hydroxy-FDP, a subsequent 1,10-ring closure has been proposed

• previously [29]. However, the presence of monocyclic products indicates that this second ring closure does not occur with 12-methoxy-FDP (12). It is suggested that the 12-methoxy group enforces an orientation of the distal 10,11-double bond that is not conducive to the second ring closure. Subsequent

Cyclopropanation–ring expansion of 3-chloroindoles with α-halodiazoacetates: novel synthesis of 4-quinolone-3-carboxylic acid and norfloxacin

• Sara Peeters,
• Linn Neerbye Berntsen,
• Pål Rongved and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2019, 15, 2156–2160, doi:10.3762/bjoc.15.212

• unit. The common denominator for three of the routes (Grohe and Heitzer [29], Gould and Jacobs [30] and Long [31]) is that they consist of ring-closure reactions to form the quinolone ring system. The fourth one (Reddy) utilizes oxidative ring cleavage of the indole ring followed by condensation [32

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• of 1,4-disubstituted 1,2,3- triazole units [19][20][21][22][23][24]. Macrocyclic ring closure can be achieved by the CuAAC of building blocks functionalized with both azide and alkyne, using [1 + 1], [2 + 2], [n + n] strategies depending on how much triazoles are needed to be included in the

• macroring. A second strategy is the macrocyclization of an acyclic precursor containing pre-functionalized triazole by other ring closure methods such as Grubbs metathesis [25] and amidation reactions. The macrocyclization is normally followed by N-alkylation (often methylation) leading to the synthesis of

Synthesis and properties of sulfur-functionalized triarylmethylium, acridinium and triangulenium dyes

• Marco Santella,
• Eduardo Della Pia,
• Jakob Kryger Sørensen and
• Bo W. Laursen

Beilstein J. Org. Chem. 2019, 15, 2133–2141, doi:10.3762/bjoc.15.210

• functionalities were synthesized and their optical properties were studied. The sulfur functionalities were introduced by aromatic nucleophilic substitution of methoxy groups in triarylmethylium cations with ethanethiol followed by partial or full ring closure of the ortho positions with nitrogen or oxygen

• amine at room temperature. Further ring closure to two oxygen bridges in acridinium compounds 4a and 4b to the corresponding triangulenium dyes S3-ADOTA+ (5a,b) was achieved by heating in molten pyridine hydrochloride (Scheme 2). It is noteworthy that the ethylthio ether linkages remained intact upon

• treatment with molten PyrHCl, which was found to result in complicated mixtures of dealkylated byproducts when these conditions were applied on dialkylamino-substituted carbenium systems [18]. The direct ring closure of 1 in PyrHCl yielded in a similar manner the sulfur-functionalized trioxatriangulenium

Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts

• Kenta Tanaka,
• Yuta Tanaka,
• Mami Kishimoto,
• Yujiro Hoshino and
• Kiyoshi Honda

Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208

• hexafluorophosphoric acid (Scheme 1a and 1b) [3][4][9][10], oxidation of thioxanthene in the presence of PbO2 followed by dehydration by tetrafluoroboric acid [1], the reaction of 4,4’-bis(dimethylamino)diphenylmethane with sulfur in the presence of ZnCl2 [11], and the ring-closure reaction of diaryl sulfide in the

Synthesis of benzo[d]imidazo[2,1-b]benzoselenoazoles: Cs₂CO₃-mediated cyclization of 1-(2-bromoaryl)benzimidazoles with selenium

• Mio Matsumura,
• Yuki Kitamura,
• Arisa Yamauchi,
• Yoshitaka Kanazawa,
• Yuki Murata,
• Tadashi Hyodo,
• Kentaro Yamaguchi and
• Shuji Yasuike

Beilstein J. Org. Chem. 2019, 15, 2029–2035, doi:10.3762/bjoc.15.199

• University, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan 10.3762/bjoc.15.199 Abstract The synthesis of benzimidazo[2,1-b]benzoselenoazoles is described. The novel ring-closure reaction of 1-(2-bromoaryl)benzimidazoles with Se powder is promoted by Cs2CO3 (2 equiv) in DMF at 150 °C. Moreover, the obtained

• , imidazo[2,1-b]selenoazoles, in which imidazole and selenophene are condensed, have been synthesized, and it was described in a patent that imidazo[2,1-b]benzoselenazole-3-acetamide derivatives have anticonvulsant activity [5]. Three ring closure reactions for the synthesis of imidazo[2,1-b]selenoazole

• ring closure reaction using N-alkynyl-2-alkylselanylimidazoles and I2 (Scheme 1, reaction 2) [7]. Moreover, Punniyamurthy et al. reported the synthesis of benzo[d]imidazo[2,1-b]benzoselenoazoles using an oxidative cyclization by reacting 1,3-diarylselenourea with (diacetoxyiodo)benzene (Scheme 1

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• N-(1-phenylethyl)aziridine-2-methanols 7 Aziridine alcohols 7 are usually prepared by LiAlH4 reduction of the corresponding esters 5 [22][35][36] although a milder method with a NaBH4 and LiCl mixture was also elaborated [37]. A multistep synthesis of (2S,1'R)-7 employing the aziridine ring closure

• lithium enolate of methyl 4-methoxyphenylacetate would give the β-hydroxyester 169 which when treated with Lewis acid experienced the aziridine ring cleavage with simultaneous dihydrofuran-2-one ring closure to produce 170 contaminated with small amounts of the corresponding furan-2(5H)-one 171

• with AD-mix-β provided an inseparable 82:18 mixture of diastereoisomers with the diol 196 as a major product. Silylation of the terminal hydroxy group was followed by mesylation of a secondary one to facilitate the piperidine ring closure triggered by hydrogenolytic removal of the chiral auxiliary to

A heteroditopic macrocycle as organocatalytic nanoreactor for pyrroloacridinone synthesis in water

• Piyali Sarkar,
• Sayan Sarkar and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2019, 15, 1505–1514, doi:10.3762/bjoc.15.152

• nanoreactor which is a single molecule as catalyst in the earliest steps of the mechanistic pathway (Figure 6). This multicomponent reaction is expected to comprise a series of condensations and subsequent ring-closure cascade reactions (Scheme 3). To demonstrate the mechanistic pathway, dimedone (2), isatin

Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction

• Pierre-Olivier Schwartz,
• Sebastian Förtsch,
• Astrid Vogt,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138

• the synthesis of dithienothiophene 1, which is mostly built up by oxidative dehydrocoupling of 3,3’-dithienyl sulfide or ring-closure reactions of brominated thiophenes with ethyl mercaptoacetate, are described in literature [24]. For comparability to the selenophene-containing triacenes 2–4, we

• reinvestigated the synthesis of DTT 1 by using a Cu-catalyzed C–S cross-coupling reaction with potassium sulfide (K2S) as sulfur source [29]. The best results for this C–S ring-closure reaction were achieved by reacting 3,3’-diiodo-2,2’-bithiophene (5) [30] with the system K2S and copper iodide (CuI) as catalyst

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• to the rigid nature of the steroidal and aryl components, a flexible diamine was required to facilitate the macrobicycle ring closure. As before, pseudo-dilution conditions were employed by the simultaneous slow addition of the three bifunctional components. Conclusion We have demonstrated that MCRs

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 1008–1019, doi:10.3762/bjoc.15.99

• , but also α-himachalene (2), γ-himachalene (3), longifolene (4), longicyclene (5), and α-longipinene (6) are traditionally considered to be derived from the himachalyl cation (B) [8][37] (Scheme 2). Whereas 1–3 are simple deprotonation products of B, 4 and 5 require a further 3,7-ring closure, leading

• to the non-classical cation C, which is a derivative of the 2-norbornyl cation [38]. This system either collapses by deprotonation at the methyl group to longifolene (4), or by deprotonation at C-4 with formation of a cyclopropane ring to longicyclene (5). Starting from B, a 2,7-ring closure and

• secondary cation D, which either stabilises by 2,10-ring closure to give the caryophyllenyl cation E that can be deprotonated at the methyl group to yield 9-epi-(E)-β-caryophyllene (7), or D undergoes a 1,3-hydride shift to the allylic cation F. Deprotonation leads to γ-humulene (8), but a 1,6-ring closure