Unusual highly diastereoselective Rh(II)-catalyzed dimerization of 3-diazo-2-arylidenesuccinimides provides access to a new dibenzazulene scaffold

• Anastasia Vepreva,
• Alexander S. Bunev,
• Andrey Yu. Kudinov,
• Grigory Kantin,
• Mikhail Krasavin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2022, 18, 533–538, doi:10.3762/bjoc.18.55

• Federal University, Kaliningrad 236041, Russian Federation 10.3762/bjoc.18.55 Abstract Formation of unusual unsymmetrical dimers or/and indenes via Rh2(esp)2-catalyzed decomposition of 3-diazo-2-arylidenesuccinimides has been investigated. The reaction proceeded under mild conditions, and its result was

• byproducts. For the 3-methoxy-substituted DAS 1n, the main reaction outcome was the unimolecular cyclization, leading to a mixture of regioisomeric indenes (Table 1, entry 14) while the target dimer 2n was obtained in low (12%) yield. A similar result was obtained earlier in the study of DAS in the reaction

• with nitriles [8]. An unexpected and interesting result was the exclusive formation of indenes 3 during the catalytic decomposition of DAS containing an ortho-substituted phenyl group at the nitrogen atom (Table 1, entries 15–17). In all three cases, compounds 3 were obtained in moderate yields, while

Facile and innovative catalytic protocol for intramolecular Friedel–Crafts cyclization of Morita–Baylis–Hillman adducts: Synergistic combination of chiral (salen)chromium(III)/BF₃·OEt₂ catalysis

• Karthikeyan Soundararajan,
• Helen Ratna Monica Jeyarajan,
• Raju Subimol Kamarajapurathu and
• Karthik Krishna Kumar Ayyanoth

Beilstein J. Org. Chem. 2021, 17, 2186–2193, doi:10.3762/bjoc.17.140

• -substituted-1H-indenes from unique substrates of Morita–Baylis–Hillman adducts via an easy operating practical procedure. Keywords: boron trifluoride etherate; chiral (salen)chromium(III); intramolecular Friedel–Crafts cyclization; Morita–Baylis–Hillman adducts; substituted-1H-indenes; Introduction

• -carboxylates [9], indenes [10][11][12][13] and indanones [14]. However, most of the reported Friedel–Crafts reactions utilize either strong Lewis acid catalysts or severe reaction conditions resulting in low yield, unwanted byproducts and tedious workup methodologies [15][16]. Therefore, developing an

• Basavaiah et al. [10] on the phosphorous pentoxide-catalysed synthesis of indene using alkoxy-substituted MBH adducts. Later Shanmugam et al. [11] reported a Mont. K10-catalysed synthesis of indenes from similar alkoxy MBH adducts. Thereafter Lee et al. [12] and Xu et al. [13] synthesised indenes in

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

• Jan Bartáček,
• Jan Svoboda,
• Martin Kocúrik,
• Jaroslav Pochobradský,
• Alexander Čegan,
• Miloš Sedlák and
• Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

• the addition of the boronic acid to the β-(2-hydroxyaryl)enone could be oxidized to afford optically pure 4-phenylchroman-2-one (Scheme 1). Also in 2007, Miyaura and co-workers presented the synthesis of enantioenriched 1-aryl-1H-indenes by a tandem 1,4-addition of arylboronic acids to enones and

• β-(2-hydroxyaryl)enones [34]. Synthesis of enantiomerically enriched 1-aryl-1H-indenes [36]. Stepwise addition of arylboronic acids to electron-rich chalcones and Bayer–Villiger oxidation [3]. Synthesis of 4-aryldihydrocoumarins by stepwise 1,4-addition and Bayer–Villiger oxidation [3]. First report

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• indenes 39a–c from the α-(trifluoromethyl)allyl-substituted benzyl alcohols 38a–c in strong acids has been reported (Scheme 9) [59]. The significant rate retardation observed upon the addition of further CF3 groups, illustrated by the need for harsh reaction conditions, strongly supports the formation of

• delocalized α-(trifluoromethyl)carbenium ions 40a–c. Vasilyev et al. also investigated this Nazarov electrocyclization for the synthesis of indene derivatives. Thus, a variety of indenes 42 could be readily obtained from α-(trifluoromethyl)allyl-substituted benzyl alcohols 41a or the corresponding silyl

• ethers 41b upon the reaction in a dichloromethane solution of sulfuric acid or triflic acid [60][61]. The authors also reported that indenes 42 could undergo a subsequent Friedel–Crafts alkylation when 41b was reacted in the presence of an external aromatic partner Ar’H in pure triflic acid. Thus, a

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• cyclobutene and several cationic intermediates and mainly yield 2-(1-phenylvinyl)indenes. In a similar reaction cascade, a fulvene derivative was obtained with 1,4-diphenylbutadiene as the substrate. Keywords: alkynes; aromatic substitution; cyclization; cycloaddition; iminium salts; Introduction In recent

• -substituted iminium groups with electron-rich (hetero)aromatics are known [18][24]. Furthermore, 1-(trifluoromethyl)indenes have recently been generated by cationic cyclization of β-aryl trifluoromethyl enones under superacid conditions [42][43][44]. Styrenes are also known to behave as dienes in [4 + 2

• NOESY NMR experiments and confirmed by an X-ray structure determination (see Figure 3). A mechanistic scheme for the formation of indenes 12 and benzo[a]fluorenes 13 is proposed in Scheme 5. The electrophilic propyn-1-iminium ion 1a adds chemoselectively (by conjugate addition) and regioselectively

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• their work, they also utilized an important chemical attribute of cetylammonium bromide (CTAB) – namely, CTAB forms surfactant-assembled lipophilic nanoreactors stable in organic solvents, which could be used for regioselective functionalization of indenes. Therefore, they investigated the

Unusual traits of cis and trans-2,3-dibromo-1,1-dimethylindane on the way from 1,1-dimethylindene to 2-bromo-, 3-bromo-, and 2,3-dibromo-1,1-dimethylindene

• Rudolf Knorr,
• David S. Stephenson,
• Ernst Lattke,
• Petra Böhrer and
• Jakob Ruhdorfer

Beilstein J. Org. Chem. 2016, 12, 1178–1184, doi:10.3762/bjoc.12.113

• -bromo-1,1-dimethylindene. Keywords: base-free dehydrobromination; cis/trans stereochemistry; five-membered ring conformation; indenes; NMR couplings; Introduction The basic mechanistic features of competing suprafacial and antarafacial additions of elemental bromine to an olefin are reasonably well

Indenopyrans – synthesis and photoluminescence properties

• Andreea Petronela Diac,
• Ana-Maria Ţepeş,
• Albert Soran,
• Ion Grosu,
• Anamaria Terec,
• Jean Roncali and
• Elena Bogdan

Beilstein J. Org. Chem. 2016, 12, 825–834, doi:10.3762/bjoc.12.81

• sciences. Besides, the annelated cyclic indenes containing N or O heteroatoms are the main structural frameworks of several natural alkaloids [1], while indenopyran derivatives were found to be valuable substrates for the synthesis of various compounds with biological activity [2][3]. Some indeno[1,2-c

Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study

• Mateo Alajarin,
• Marta Marin-Luna,
• Pilar Sanchez-Andrada and
• Angel Vidal

Beilstein J. Org. Chem. 2016, 12, 260–270, doi:10.3762/bjoc.12.28

• Academy, Base Aerea de San Javier, C/ Coronel López Peña s/n, 30720, Santiago de la Ribera, Murcia, Spain 10.3762/bjoc.12.28 Abstract 6-Phenylfulvenes bearing (1,3-dioxolan or dioxan)-2-yl substituents at ortho position convert into mixtures of 4- and 9-(hydroxy)alkoxy-substituted benz[f]indenes as

• result of cascade processes initiated by a thermally activated hydrogen shift. Structurally related fulvenes with non-cyclic acetalic units afforded mixtures of 4- and 9-alkoxybenz[f]indenes under similar thermal conditions. Mechanistic paths promoted by an initial [1,4]-, [1,5]-, [1,7]- or [1,9]-H shift

• to isolate the benz[f]indenes 5a and 6a, in a relative 2:1 ratio and a poor global yield (34%). We next tested the same and similar processes in a microwave apparatus. As presumed, conversions of a series of acetal-fulvenes 3a–f under 120 W microwave irradiation at 120 °C in DMSO required much

Facile synthesis of functionalized tetrahydroquinolines via domino Povarov reactions of arylamines, methyl propiolate and aromatic aldehydes

• Jing Sun,
• Hong Gao,
• Qun Wu and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2012, 8, 1839–1843, doi:10.3762/bjoc.8.211

• dienophiles, vinyl enol ethers, vinyl enamides, vinyl sulfides, cyclopentadienes, indenes, alkynes and enamines have been mostly used in this method [12][13][14][15][16][17][18][19][20][21][22]. β-Enamino esters [23][24][25][26], which may be readily generated in situ by the addition of a primary amine to

Synthetic approaches to multifunctional indenes

• Neus Mesquida,
• Sara López-Pérez,
• Immaculada Dinarès and
• Ermitas Alcalde

Beilstein J. Org. Chem. 2011, 7, 1739–1744, doi:10.3762/bjoc.7.204

• multifunctional indenes with at least two different functional groups has not yet been extensively explored. Among the plausible synthetic routes to 3,5-disubstituted indenes bearing two different functional groups, such as the [3-(aminoethyl)inden-5-yl)]amines, a reasonable pathway involves the (5-nitro-3

• ; amides; indanones; indenes; organometallic reagents; Introduction Compounds with an indene core are of great interest as precursors of metallocene complexes for catalytic polymerization processes, as well as being present in N-heterocyclic carbene ligands and functional materials [1][2][3][4][5][6][7][8

• ][9]. In addition, indene-based structures are a source of bioactive compounds in drug discovery and development [10][11][12][13][14][15][16][17][18]. The routes to access multiply substituted indenes with at least two different functional groups (FGs) are generally complex, and the synthetic

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• indenes 40 is observed upon introduction of ester and phenyl substituents on the cyclopropene (Scheme 7). AuPR3NTf2 complexes (PR3 = 41–45) are selective catalysts for the intermolecular hydroalkoxylation of electron-poor alkynes of type R−C≡C−EWG and dimethyl acetylenedicarboxylate [33]. In reactions of

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• proceed over indene formation, since it is required to stabilize the intermediate carbocation. As before, the only difference in the product structure is whether H or I has been incorporated. Sanz and co-workers reported in 2010 that indenes were formed from o-alkynylstyrenes in the presence of AuCl(PPh3

• , although all ligands tested with the gold complexes and silver salt AgSbF6 allowed full conversion to the indene. From these results, Sanz and co-workers also reported the corresponding halocyclization of o-alkynylstyrenes to yield 3-halo-1H-indenes by employing NIS as the iodonium source (Scheme 7b) [92

• of an asymmetric halocyclization towards indenes remains an ongoing task [93][94][95][96]. Notably, 1,5-enynes that do not contain an aryl system react in quite a similar manner when disubstituted at C1. For example, Michelet and co-workers reported the diastereoselective cycloisomerization of 1,5

Fine-tuning alkyne cycloadditions: Insights into photochemistry responsible for the double-strand DNA cleavage via structural perturbations in diaryl alkyne conjugates

• Wang-Yong Yang,
• Samantha A. Marrone,
• Nalisha Minors,
• Diego A. R. Zorio and
• Igor V. Alabugin

Beilstein J. Org. Chem. 2011, 7, 813–823, doi:10.3762/bjoc.7.93

• ][38][39][40][41][42][43][44] (akin to such well-known DNA cleavers as enediyne antibiotics) [45][46] or C1–C5 cyclization [47][48][49][50][51][52] (Figure 2). In the latter process, which transforms enediynes into indenes, four hydrogens are transferred from the environment (two as H-atoms and two as

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• aziridines. Gold-catalyzed synthesis of disubstituted cyclohexadienes. Gold-catalyzed synthesis of indenes. Gold-catalyzed [n + m] annulation processes. Gold-catalyzed generation of 1,4-dipoles. Gold-catalyzed synthesis of repraesentin F. Gold-catalyzed ring expansion of cyclopropyl 1,6-enynes. Gold

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• vinylidenecyclopropanes, Shi et al. investigated the behaviour of 1-(2,2-diarylvinyl)-2-phenylcyclopropenes in the presence of gold catalysts [20]. Upon treatment with [(Ph3P)AuOTf], vinylcyclopropene 18 was found to produce a mixture of regioisomeric indenes 19 and 20 in a 75:25 ratio (99%). The use of AgOTf alone led

• -withdrawing substituents on the benzene rings. The corresponding indenes 26 were obtained in good to excellent yields (85–99%) under the previously optimized conditions (Scheme 12) [20]. In the absence of substituents at C3 (R3 = R4 = H), or when a single substituent was attached to this carbon (R3 = Me, R4

• reported. In 2009, Wang et al. demonstrated that [(Ph3P)AuOTf] could smoothly catalyze the isomerization of a variety of 3-substituted 1,2,3-triphenylcyclopropenes 27 into 3-substituted 1,2-diphenyl-1H-indenes 28 [21]. The rearrangement occurred rapidly (20–40 min) for substrates 27a–27e and indenes 28a

Radical cascades using enantioenriched 7-azabenzonorbornenes and their applications in synthesis

• David M. Hodgson and
• Leonard H. Winning

Beilstein J. Org. Chem. 2008, 4, No. 38, doi:10.3762/bjoc.4.38

• from 7-azabenzonorbornadienes gives 3-exo-substituted 2-aza-5,6-benzonorbornenes, which in some cases undergo isomerisation to (aminomethyl)indenes. The starting xanthates are accessible in good yields and high enantiomeric ratios via asymmetric hydroboration of (aryne/pyrrole-derived) 7

• some degree of isomerisation to (aminomethyl)indenes 22 and 25 respectively were observed, as indicated by the appearance of vinylic CH resonances in the 1H NMR spectra (δ 6.8–6.0). This isomerisation is presumably the result of trace acid catalysis, with the process likely proceeding via protonation

• of the nitrogen atom, followed by ring opening to a stabilised benzylic cation. 1H NMR analysis also revealed that the resulting (aminomethyl)indenes 22 and 25 degraded with time. The tandem deoxygenation–rearrangement–electrophile trapping reaction was attempted for xanthates 20 and 23 using