Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• substituents with different electronic properties (Scheme 2). Interestingly, we found that oxidative cyclization can occur from both double bond isomers. In addition, a reductive cyclization was discovered in bis(benzonitrile)-substituted DTEs and also in a DTE with an extended π-system. Results and Discussion

• radical cations [34][35] and simple dithienylethenes [36][37][38]. As such, we postulate an equilibrium between both E- and Z-radical cations with the latter rapidly reacting to the closed isomer. To gain a deeper mechanistic understanding of the oxidative cyclization, the evolution of the UV–vis

• reduction, a species analogous to FP was not observed (vide infra and Figure S43, Supporting Information File 1). Considering all these findings, a mechanism for the oxidative cyclization of sDTE66-Me (Scheme 3) can be derived: Starting from either open isomer fast isomerization to the same dication C2

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• reduced to Co(I) (A) in the presence of metallic Zn. The oxidative cyclization of A with alkyne 16 and CO2 affords cobaltacycle B (step a). Next, the transmetalation between B and the Zn(II) species occurs, which affords the alkenylzinc intermediate C (step b) [41], which is then reduced with Zn powder

• reaction. In a similar manner to that described for the carboxyzincation, the reduction of the Co(II) precursor to Co(I) species A in the presence of Zn metal activates the catalytic cycle. Next, the oxidative cyclization of A, alkyne 16, and acrylate 18 proceeds regioselectively, and cobaltacycle B is

• reaction mechanism for these reactions. First, the Co(II) precursor is reduced to Co(I) A by the aid of an Ir photoredox catalyst and an amine under irradiation. The oxidative cyclization of A with 23 and CO2 affords cobaltacycle B (step a). Next, the protonation of B affords an intermediate C (step b

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

• Fateh V. Singh,
• Priyanka B. Kole,
• Saeesh R. Mangaonkar and
• Samata E. Shetgaonkar

Beilstein J. Org. Chem. 2018, 14, 1778–1805, doi:10.3762/bjoc.14.152

• stereoselective synthesis. Additionally, the applications of these reagents in natural product synthesis are also covered. Keywords: hypervalent iodine reagents; iodoarenes; natural products; oxidative cyclization; spirocyclic compounds; Review 1. Introduction The chemistry of spirocyclic compounds is a well

• 2.5 h (Scheme 11). Additionally, the synthesized spirocyclic precursor 16 was transfered to (−)-tuberostemonine (40) in three chemical steps. 3. Synthesis of spirolactams 3.1. Using stoichiometric amounts of iodine(III) reagents In 1998, Ciufolini and co-workers [80] reported the oxidative cyclization

• (Scheme 12). Additionally, the same research group [81] reported the oxidative cyclization of a phenolic substrate to a spirolactam using PIDA as electrophile. In this methodology, oxazoline 43 was cyclized to spirolactam 44 in 50% yield using PIDA (15) in trifluoroethanol at room temperature (Scheme 13

Synthesis of trifluoromethylated 2H-azirines through Togni reagent-mediated trifluoromethylation followed by PhIO-mediated azirination

• Jiyun Sun,
• Xiaohua Zhen,
• Huaibin Ge,
• Guangtao Zhang,
• Xuechan An and
• Yunfei Du

Beilstein J. Org. Chem. 2018, 14, 1452–1458, doi:10.3762/bjoc.14.123

• [52][53][54][55] have been developed for accessing this exclusive class of heterocycles. In our previous works, we have realized the application of hypervalent iodine reagents for the construction of the 2H-azirine skeleton starting from enamines 2 via intramolecular oxidative cyclization (Scheme 1

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• imparted superior reactivity compared to Ishihara’s system without the need of achiral alcohols as an additive. Profitable results were obtained regarding the oxidative cyclization of phenolic derivatives 36 to spirocyclic compounds 37. Chiral hypervalent iodine reagents having binaphthyl backbones were

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• -benzotropone (11) with dimethyl barbituric acid (62) and subsequent oxidative cyclization reaction using DDQ-Sc(OTf)3 or photoirradiation under aerobic conditions afforded 61+.BF4− (Scheme 12). The pKR+ value and reduction potential of the cation 61 were studied. The relative stability of a carbocation can be

Selective carboxylation of reactive benzylic C–H bonds by a hypervalent iodine(III)/inorganic bromide oxidation system

• Toshifumi Dohi,
• Shohei Ueda,
• Kosuke Iwasaki,
• Yusuke Tsunoda,
• Koji Morimoto and
• Yasuyuki Kita

Beilstein J. Org. Chem. 2018, 14, 1087–1094, doi:10.3762/bjoc.14.94

• synthesis of lactones via the intramolecular oxidative cyclization of aryl carboxylic acids at the benzyl carbon under transition-metal-free conditions [52]. Based on our previous research and general interest in the unique reactivity of hypervalent iodine(III)–Br bonds [53][54][55][56], we report the

Hypervalent iodine-mediated Ritter-type amidation of terminal alkenes: The synthesis of isoxazoline and pyrazoline cores

• Sang Won Park,
• Soong-Hyun Kim,
• Jaeyoung Song,
• Ga Young Park,
• Darong Kim,
• Tae-Gyu Nam and
• Ki Bum Hong

Beilstein J. Org. Chem. 2018, 14, 1028–1033, doi:10.3762/bjoc.14.89

• , diverse halonium sources have been utilized for the synthesis of isoxazolines via halocyclization. Furthermore, transition metal-, visible light, and hypervalent iodine-mediated oxidative cyclization protocols provide isoxazoline backbones bearing diverse substituents such as –SR, -CF3, -OH and halogens

Transition-metal-free [3 + 3] annulation of indol-2-ylmethyl carbanions to nitroarenes. A novel synthesis of indolo[3,2-b]quinolines (quindolines)

• Michał Nowacki and
• Krzysztof Wojciechowski

Beilstein J. Org. Chem. 2018, 14, 194–202, doi:10.3762/bjoc.14.14

• (e) [15] and palladium(II) acetate-mediated oxidative cyclization of 3-(phenylamino)quinoline (f) afford quindoline [16]. Some of these syntheses require harsh conditions and multistep procedures. Another drawback of some of the known methodologies is the use of transition metal catalysts for the

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

Nucleophilic dearomatization of 4-aza-6-nitrobenzofuroxan by CH acids in the synthesis of pharmacology-oriented compounds

• Alexey M. Starosotnikov,
• Dmitry V. Shkaev,
• Maxim A. Bastrakov,
• Ivan V. Fedyanin,
• Svyatoslav A. Shevelev and
• Igor L. Dalinger

Beilstein J. Org. Chem. 2017, 13, 2854–2861, doi:10.3762/bjoc.13.277

• from chloride 4 which was treated with methanolic ammonia solution to give 2-amino-3,5-dinitropyridine (5). Oxidative cyclization of 5 under the action of PhI(OAc)2 gave ANBF in 87% overall yield (Scheme 4). The 1H NMR spectra of compound 1 in dry deuterated DMSO and acetone coincided with those

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• . [4 + 1]-Annulation of nitrosoalkenes NSA with sulfonium ylides 92. Reaction of diazo compounds 96 with nitrosoalkenes NSA. Tandem Michael addition/oxidative cyclization strategy to isoxazolines 100. Acknowledgements This work was supported by Russian Foundation for Basic Research (Grants 17-03

Preparation of imidazo[1,2-a]-N-heterocyclic derivatives with gem-difluorinated side chains

• Layal Hariss,
• Kamal Bou Hadir,
• Mirvat El-Masri,
• Thierry Roisnel,
• René Grée and
• Ali Hachem

Beilstein J. Org. Chem. 2017, 13, 2115–2121, doi:10.3762/bjoc.13.208

• % yield (Table 2, entry 1). Having these optimized conditions in hand, and to explore the substrate scope, different substituted 2-aminopyridines were successfully employed to afford the tandem oxidative cyclization products 7 in 32–65% yields. On the other hand, enones 6 with two different R groups

Facile synthesis of indolo[3,2-a]carbazoles via Pd-catalyzed twofold oxidative cyclization

• Chao Yang,
• Kai Lin,
• Lan Huang,
• Wei-dong Pan and
• Sheng Liu

Beilstein J. Org. Chem. 2016, 12, 2490–2494, doi:10.3762/bjoc.12.243

• twofold oxidative cyclization. Findings The oxidative biaryl coupling reaction was originally described over 30 years ago using stoichiometric palladium(II) [9][10]. Quite recently, the reaction has been developed to proceed catalytically and widely applied as an atom economic approach to carbazoles [11

The direct oxidative diene cyclization and related reactions in natural product synthesis

• Juliane Adrian,
• Leona J. Gross and
• Christian B. W. Stark

Beilstein J. Org. Chem. 2016, 12, 2104–2123, doi:10.3762/bjoc.12.200

• Juliane Adrian Leona J. Gross Christian B. W. Stark Fachbereich Chemie, Institut für Organische Chemie, Universität Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany 10.3762/bjoc.12.200 Abstract The direct oxidative cyclization of 1,5-dienes is a valuable synthetic method for the (dia

• . Likewise, syntheses of fragments of natural products applying an oxidative cyclization protocol [1][2] and sequential epoxidation/cyclization procedures [3] are not in the scope of this article and are therefore not covered. Previous review articles concerning oxidative diene cyclization chemistry can be

• considered in complement [4][5][6]. Oxidative cyclization – Historical background In 1924 Kötz and Steche reported on an investigation of the constitution of the monoterpene geraniol (1, R = H) [7]. Though the overall structure was known at that time, the position of one of the two C–C-double bonds within

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• rhodium first undergoes oxidative cyclization with the vinylcyclopropane prior to alkyne insertion. The asymmetric enyne cycloisomerization reaction has been shown to be instrumental in the construction of medicinal chemistry targets. For example, the Fürstner group realized that gold catalysis would be

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• xeniaethers. An alternative biosynthetic pathway proposed by Schmitz and van der Helm involves the direct formation of the nine-membered carbocyclic ring via oxidative cyclization of geranyllinalool (34) [2], which is formed from GGPP (28) by enzymatic hydrolysis of the pyrophosphate unit and allylic

A new and convenient synthetic way to 2-substituted thieno[2,3-b]indoles

• Roman A. Irgashev,
• Arseny A. Karmatsky,
• Gennady L. Rusinov and
• Valery N. Charushin

Beilstein J. Org. Chem. 2015, 11, 1000–1007, doi:10.3762/bjoc.11.112

• , including oxidative cyclization of indolin-2-thiones 1 [20], radical or palladium catalyzed cyclization of 3-(2-bromoindol-3-yl)acrylonitriles 2 [21][22], intramolecular CH/NH-coupling in benzo[b]thiophenes 3 [23], AlCl3 catalyzed recyclization of 2-(2-isothiocyanatophenyl)furanes 4 [24], reductive

Eosin Y-catalyzed visible-light-mediated aerobic oxidative cyclization of N,N-dimethylanilines with maleimides

• Zhongwei Liang,
• Song Xu,
• Wenyan Tian and
• Ronghua Zhang

Beilstein J. Org. Chem. 2015, 11, 425–430, doi:10.3762/bjoc.11.48

• as a photocatalyst has been developed. The metal-free protocol involves aerobic oxidative cyclization via sp3 C–H bond functionalization process to afford good yields in a one-pot procedure under mild conditions. Keywords: aerobic oxidative cyclization; C–H functionalization; Eosin Y; photoredox

• tends to form the iminium ion by one electron oxidation (Scheme 1) [39][40][41]. In the context of this research background, we investigated the α-aminoalkyl radical route to achieve the aerobic oxidative cyclization of N,N-dimethylanilines with maleimides to form the corresponding tetrahydroquinoline

• presented the same reaction using [Ru(bpy)3]3+ as photoredox catalyst under irradiation with visible light next year [44]. Herein, we show an environmentally friendly aerobic oxidative cyclization methodology that avoids the use of metal catalysts and makes full use of air as oxidant. Results and Discussion

Photovoltaic-driven organic electrosynthesis and efforts toward more sustainable oxidation reactions

• Bichlien H. Nguyen,
• Robert J. Perkins,
• Jake A. Smith and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2015, 11, 280–287, doi:10.3762/bjoc.11.32

• condensation. Solar-driven oxidative cyclization with a second nucleophile. Acknowledgements We thank the National Science Foundation (CHE-1151121, CBET-1262176) and (CHE-1240194/CenSURF) for their generous support of our work.

Come-back of phenanthridine and phenanthridinium derivatives in the 21st century

• Lidija-Marija Tumir,
• Marijana Radić Stojković and
• Ivo Piantanida

Beilstein J. Org. Chem. 2014, 10, 2930–2954, doi:10.3762/bjoc.10.312

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

Beilstein J. Org. Chem. 2014, 10, 2858–2873, doi:10.3762/bjoc.10.303

• certain functional groups [3][4]. In the last decades, research in this field has therefore been focused on the development of more efficient and selective strategies. In the current focus of heterocycle synthesis are C,H-activation with transition metal catalysts [5][6][7][8], oxidative cyclization using

Magnesium bis(monoperoxyphthalate) hexahydrate as mild and efficient oxidant for the synthesis of selenones

• Andrea Temperini,
• Massimo Curini,
• Ornelio Rosati and
• Lucio Minuti

Beilstein J. Org. Chem. 2014, 10, 1267–1271, doi:10.3762/bjoc.10.127

• obtained in good yield by the oxidative cyclization of the acylamino phenyl selenide 1g with MMPP in methanol (Table 2, entry 4) although in lower yield than reported before (90% [14]). As reported in Table 2 (entries 5 and 6), the N-tosyl-1,3-oxazolidin-2-one [11] 3h and the N-benzoyl-1,3-oxazolidin-2-one

• the oxidative-cyclization reaction of 1j not only favoured the oxidation reaction, but also suppressed the β-elimination side reaction of the selenoxide intermediate [14]. Thus tetrahydrofuran 3j was obtained in 69% yield (Table 2, entry 7) as the sole product. It is interesting to note that N

• bioactive molecules is currently under investigation. General transformation of selenides to selenones. Phenylselenone 2 as useful leaving group for the synthesis of different organic molecules. Oxidation of selenides 1a–d to selenones 2a–d with MMPP. Oxidative cyclization with MMPP of functionalized

Synthesis of ethoxy dibenzooxaphosphorin oxides through palladium-catalyzed C(sp²)–H activation/C–O formation

• Seohyun Shin,
• Dongjin Kang,
• Woo Hyung Jeon and
• Phil Ho Lee

Beilstein J. Org. Chem. 2014, 10, 1220–1227, doi:10.3762/bjoc.10.120

• ). After examination of the reaction temperature (Table 1, entries 11–13) and time (Table 1, entries 14–16), the oxidative cyclization using PhI(OAc)2 (2 equiv) and KOAc (2 equiv) in the presence of Pd(OAc)2 (10 mol %) and L9 (30 mol %) gave the best result under aerobic conditions, affording 2a in 61

• phenylphosphonic acid monoethyl ester 1i underwent the Pd-catalyzed oxidative cyclization regioselectively at the sterically less hindered position to afford the desired dibenzooxaphosphorin oxide 2i in 70% yield. We were pleased to obtain 2j by a Pd-catalyzed oxidative cyclization of 1-naphthyl-substituted

• phenylphosphonic acid monoethyl ester 1j. 2-(Aryl)phenylphosphonic acid monoethyl esters 1k, 1l and 1m with an electron-withdrawing fluoro or chloro group on the phenyl ring were subjected to the oxidative cyclization to deliver the desired products 2k, 2l and 2m in yields ranging from 54% and 64%. In particular

IBD-mediated oxidative cyclization of pyrimidinylhydrazones and concurrent Dimroth rearrangement: Synthesis of [1,2,4]triazolo[1,5-c]pyrimidine derivatives

• Caifei Tang,
• Zhiming Li and
• Quanrui Wang

Beilstein J. Org. Chem. 2013, 9, 2629–2634, doi:10.3762/bjoc.9.298

• Caifei Tang Zhiming Li Quanrui Wang Department of Chemistry, Fudan University, 200433 Shanghai, P. R. of China 10.3762/bjoc.9.298 Abstract Oxidative cyclization of 6-chloro-4-pyrimidinylhydrazones 4 with iodobenzene diacetate (IBD) in dichloromethane gives rise to [1,2,4]triazolo[4,3-c]pyrimidine

• chloro-substituted pyridines and related heterocycles, from which the triazolopyridines and other related fused heterocycles can be obtained after oxidative cyclization [14]. In accordance with the significance shown by triazolopyrimidines, the development of complementary and simple synthetic methods

• synthesis of novel [1,2,4]triazolo[1,5-a]pyrimidine derivatives by iodobenzenediacetate (IBD)-mediated oxidative cyclization of suitable N-benzylidene-N′-pyrimidin-2-yl hydrazine precursors, followed by a Dimroth rearrangement [20]. We envisioned that our aldehyde chloropyrimidinylhydrazones 4 would undergo