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

• substrate for the synthesis of natural product (+)-biscarvacrol (157). Koag and Lee [140] reported the synthesis of a spiroketal by radical cyclization of a steroidal alkylamine in presence of PIDA (15) as oxidant and molecular iodine in dichloromethane at low temperature. It is an example of hypoiodite

• -mediated radical cyclization wherein the oxazaspiroketal moiety is formed which is further used as key intermediate for the synthesis of the natural product cephalostatin. Additionally, spiroketals 159 were also synthesised by enatioselective spirocyclization of ortho-substituted phenols 158 using similar

One-pot preparation of 4-aryl-3-bromocoumarins from 4-aryl-2-propynoic acids with diaryliodonium salts, TBAB, and Na₂S₂O₈

• Teppei Sasaki,
• Katsuhiko Moriyama and
• Hideo Togo

Beilstein J. Org. Chem. 2018, 14, 345–353, doi:10.3762/bjoc.14.22

• acid-catalyzed reaction of phenols and propynoic acids [22] and the (−)-riboflavin-catalyzed photochemical reaction of cinnamic acids [23] were reported recently. Moreover, the use of radical cyclization for the construction of the coumarin skeleton has become widespread. Examples include the radical

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

• addition of dicarbonyl compounds to a nitrosoalkene followed by a silver-mediated radical cyclization of the resulting oximes 6 to final isoxazolines 100. Importantly, the reaction is well-tolerated by various substituents both in halooxime and in dicarbonyl compounds producing isoxazolines 100 in moderate

Brønsted acid-mediated cyclization–dehydrosulfonylation/reduction sequences: An easy access to pyrazinoisoquinolines and pyridopyrazines

• Ramana Sreenivasa Rao and
• Chinnasamy Ramaraj Ramanathan

Beilstein J. Org. Chem. 2017, 13, 428–440, doi:10.3762/bjoc.13.46

• for the synthesis of many alkaloids (Figure 1) [16]. To synthesize pyrazinoisoquinoline and its derivatives, various approaches such as the Ugi multicomponent reaction [17] amidoalkylation [18][19], N-acyliminium ion cyclization [20] and a radical cyclization [21] have been reported. To this end

Cp₂TiCl/D₂O/Mn, a formidable reagent for the deuteration of organic compounds

• Antonio Rosales and
• Ignacio Rodríguez-García

Beilstein J. Org. Chem. 2016, 12, 1585–1589, doi:10.3762/bjoc.12.154

• epoxides [2][27][37], ozonides [29], ketones [31][32], activated halides [30][31][32], alkenes and alkynes [33]. Several examples are presented in Scheme 3. The results show that the combination Cp2TiCl/D2O/Mn is able to promote and/or catalyze deuteration of organic compounds by reduction or radical

• cyclization using reagents that are cheap, abundant and environmentally friendly. Certainly, this new methodology of deuteration will contribute to the synthesis of new deuterated organic compounds with applications as internal standards, pharmaceutical drugs and new materials, among others. Conclusion In

Cascade alkylarylation of substituted N-allylbenzamides for the construction of dihydroisoquinolin-1(2H)-ones and isoquinoline-1,3(2H,4H)-diones

• Ping Qian,
• Bingnan Du,
• Wei Jiao,
• Haibo Mei,
• Jianlin Han and
• Yi Pan

Beilstein J. Org. Chem. 2016, 12, 301–308, doi:10.3762/bjoc.12.32

• , these cascade radical cyclization reactions are of general use for the preparation of 4-alkyldihydroisoquinolin-1(2H)-one derivatives 5. The substrates bearing methyl, methoxy, halo and trifluoromethyl groups on the aromatic ring all worked well in the reaction, providing the target products with 31–65

• corresponding products (5ae1–5ae5) with 42% total yield. To extend the synthetic utility of this radical cyclization reaction, N-methacryloyl-N-methylbenzamide derivatives 6 were then tried as substrates for this reaction (Scheme 4). It should be mentioned that only a few radical precursors, such as the TMSCF3

• (Scheme 5c). This discloses that the cleavage of the C(sp3)−H bond to form the radical may be involved in the turnover-limiting steps of this procedure. Based on the previous radical cyclization reactions [44][47][48] and the results obtained above, a plausible mechanism accounting for this cascade

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

• plumisclerin A by Pauson–Khand annulation and SmI2-mediated radical cyclization [59]. The xenicane-related diterpenoid (isolated from the same marine organism as xenicin 116) possesses a complex ring system that is proposed to be biosynthetically derived from the xenicin diterpenoid 116 by an intramolecular [2

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• by treating the binicotinic acid with methanol and sulfuric acid. The resulting product was transformed into a 2-haloanilide under Weinreb conditions, namely trimethylaluminium and 2-haloaniline. Subarine (37) was subsequently obtained from the radical cyclization of the haloanilide derivative in the

Fates of imine intermediates in radical cyclizations of N-sulfonylindoles and ene-sulfonamides

• Hanmo Zhang,
• E. Ben Hay,
• Stephen J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2015, 11, 1649–1655, doi:10.3762/bjoc.11.181

• ; radical cyclization; radical fragmentation; spiro-indoles; Introduction Radical additions and cyclizations of ene-sulfonamides are useful reactions in a number of settings. The primary products of these reactions, α-sulfonamidoyl radicals, are often thought to undergo elimination reactions of sulfonyl

• ] = 0.01 M) led to complete conversion after 1 h of heating. Solvent evaporation and flash chromatography provided spiro-3,3'-biindoline 8 in 47% isolated yield. As with the formation of 5a–c in Scheme 1, an imine is presumably formed by aryl radical cyclization and then sulfonyl radical elimination, but

• mechanism aside, the take home message is N-sulfonylindoles undergo both radical cyclization and elimination; however, the resulting spirocyclic N-arylimines may be susceptible to further reduction to the amine depending on the carbon substituent of the imine. In contrast, related spirocyclic imines with N

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• ). Molander and Harris developed the samarium(II) iodide-mediated cyclization of α,β-unsaturated esters and amides [167] (Scheme 20). Previous methods for the cyclization of alkyl halides and α,β-unsaturated carbonyl systems include: (1) tin-mediated radical cyclization [168] or (2) nucleophilc cyclization

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

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

• reactions is presented and discussed in this review. Keywords: anodic cyclization; electrosynthesis; heterocycle; olefin coupling; organic electrochemistry; radical cyclization; Introduction The construction of heterocyclic cores undoubtedly represents a highly important discipline of organic synthesis

• electrochemical reaction leads to an Umpolung of the functional group with the lower redox potential, triggering the ring-closure reaction between a nucleophilic and an electrophilic site. Another possibility for an intramolecular ring closure is represented by electrochemically induced radical cyclization

• , recent efforts in electrochemical heterocycle synthesis can mostly be differentiated into anodic olefin coupling (section 1.1), radical cyclization (section 1.2), and trapping of anodically generated iminium/alkoxycarbenium ions (section 1.3). On the other hand, cycloadditions (section 2.1), sequential

Cyclization–endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst

• Nathan J. Gesmundo and
• David A. Nicewicz

Beilstein J. Org. Chem. 2014, 10, 1272–1281, doi:10.3762/bjoc.10.128

• the reactivity of the diene with respect to its structure to better predict the mode of diene cation radical cyclization (5-exo vs 6-endo). Herein is reported an organocatalytic photoredox-mediated strategy for the endoperoxidation of 1,5-dienes using 3O2 to rapidly generate complex endoperoxide

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• coworker [200] found an intriguing example of a light mediated radical cyclization/arylvinylcyclopropane rearrangement. Subjecting cyclopropyl bromide 237 to an Ir-polypyridyl catalyst and visible light initiated the desired photoredox cascade forming a cyclopropylradical, which readily cyclized in an 5

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• ) in AcOH/CH2Cl2 produced 3-hydroperoxy-6-(2-methoxyethoxy)-3,6-dimethyl-1,2-dioxane (286) (Scheme 80) [270]. 3.11. Other methods for the synthesis of 1,2-dioxanes The di(tert-butyl)peroxalate-initiated radical cyclization of unsaturated 2-(3-hydroperoxypropyl)-6,6-dimethylbicyclo[3.1.1]hept-2-ene

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• light-mediated reductions such as reductive dehalogenation [47][48][49][50][51], reductive radical cyclization [52][53][54], reduction of activated ketones [49], and reduction of aromatic azides [55]. The third mode involves deprotonation of amine radical cation 2 to form α-amino radical 3, which is

Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

• Andreas Gansäuer,
• Meriam Seddiqzai,
• Tobias Dahmen,
• Rebecca Sure and
• Stefan Grimme

Beilstein J. Org. Chem. 2013, 9, 1620–1629, doi:10.3762/bjoc.9.185

• similar. The length of the forming bond is 2.30 Å and the angle of attack to the double bond is 108.2° in our treatment. These values are slightly different than the values used in the modeling based calculations of radical cyclization (2.34 Å and 105.8°) that were derived from values of the attack of

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives via radical pathways

• Eietsu Hasegawa,
• Minami Tateyama,
• Ryosuke Nagumo,
• Eiji Tayama and
• Hajime Iwamoto

Beilstein J. Org. Chem. 2013, 9, 1397–1406, doi:10.3762/bjoc.9.156

• hexenyl radical cyclization reactions [21], (Figure 1) [22][23][24][25][26][27][28][29][30]. For example, PET reactions of probe I with amines were observed to produce a spirocyclic ketone product while its reduction reaction induced by samarium diiodide (SmI2) gives rise to a cyclopropanol (left in

• suggest that a rapid equilibrium does indeed exist between isomeric radical intermediates 9 and 10 (Scheme 7) and that the thermodynamically less stable isomer 9 undergoes fast hexenyl-radical cyclization leading to the formation of 11 in reactions promoted by copper(II) carboxylates. On the other hand, a

• 22 and 23. However, competitive generation of 19 does not take place (Table 3, entry 4). Finally, reaction of 1c with Cu(OTf)2 leads to the formation of ring-expanded enone 20 and acetoamide 24 (Table 3, entry 5). As described above, observation of the occurrence of hexenyl-radical cyclization

A construction of 4,4-spirocyclic γ-lactams by tandem radical cyclization with carbon monoxide

• Mitsuhiro Ueda,
• Yoshitaka Uenoyama,
• Nozomi Terasoma,
• Shoko Doi,
• Shoji Kobayashi,
• Ilhyong Ryu and
• John A. Murphy

Beilstein J. Org. Chem. 2013, 9, 1340–1345, doi:10.3762/bjoc.9.151

• Technology, 5-16-1 Ohmiya, Asahi-ku, Osaka 535-8585, Japan Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK 10.3762/bjoc.9.151 Abstract A straightforward synthesis of 4,4-spirocyclic indol γ-lactams by tandem radical cyclization of iodoaryl allyl

• ; iodoaryl allyl azides; tandem radical cyclization; Introduction 4,4-Spirocyclic oxindole γ-lactams containing a quaternary carbon center are key structures for the synthesis of biologically active natural products and the related analogues [1][2][3][4]. Therefore, the development of an efficient synthesis

• -spirocyclic oxindole γ-lactams by the cycloaddition of imines and succinic anhydrides [5]. Tandem radical cyclization can also provide a powerful tool for the construction of heterocycles [6][7][8][9][10][11][12]. One of us previously reported on the construction of spirocyclic pyrrolidinyl oxindoles by the

Preparation of optically active bicyclodihydrosiloles by a radical cascade reaction

• Koichiro Miyazaki,
• Yu Yamane,
• Ryuichiro Yo,
• Hidemitsu Uno and
• Akio Kamimura

Beilstein J. Org. Chem. 2013, 9, 1326–1332, doi:10.3762/bjoc.9.149

• -carbonyl radical that underwent radical cyclization to a terminal alkyne unit. The resulting vinyl radical attacked the silicon atom in an SHi manner to give dihydrosilole. The reaction preferentially formed trans isomers of bicyclosiloles with an approximately 7:3 to 9:1 selectivity. Keywords

• : bicyclodihydrosilole; free radical; radical cascade reaction; SHi reaction; tris(trimethylsilyl)silane; Introduction Radical cyclization occupies a unique position in organic synthesis because it is a useful reaction for the construction of cyclic molecules [1][2][3][4][5][6][7][8][9][10]. The radical cascade

• radical cyclization in a 5-exo-dig mode giving vinyl radical intermediate B, which is potentially reactive for attacking the silyl group in an SHi manner to give a Me3Si radical and 2. The process from B to 2 should be very rapid. Giese and co-workers have reported that the reaction rate for a similar SHi

Exploration of an epoxidation–ring-opening strategy for the synthesis of lyconadin A and discovery of an unexpected Payne rearrangement

• Brad M. Loertscher,
• Yu Zhang and
• Steven L. Castle

Beilstein J. Org. Chem. 2013, 9, 1179–1184, doi:10.3762/bjoc.9.132

• for synthesis. Herein, we provide an account of our studies directed toward the construction of this alkaloid. Specifically, we describe our efforts to prepare advanced intermediates that could be employed in the aforementioned pyridone annulation and tandem radical cyclization processes. In the

• functional-group manipulations. Based on the aforementioned model study [11], 7-exo–6-exo tandem radical cyclization of phenyl selenoester 4 was expected to produce ketone 3. Disassembly of the pyridone moiety of 4 according to our annulation protocol [14] revealed thioester 5 as a suitable precursor. We

Formal synthesis of (−)-agelastatin A: an iron(II)-mediated cyclization strategy

• Daisuke Shigeoka,
• Takuma Kamon and
• Takehiko Yoshimitsu

Beilstein J. Org. Chem. 2013, 9, 860–865, doi:10.3762/bjoc.9.99

• have developed a new approach to key compounds 5a/5b for (−)-agelastatin A (1) synthesis, which features the iron(II)-mediated radical cyclization of N-tosyloxycarbamate, a safe azidoformate surrogate. Although somewhat moderate chemical yields of the compounds were obtained in this study, the

Direct alkenylation of indolin-2-ones by 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles: a novel approach

• Sandeep Kumar,
• Ramendra Pratap,
• Abhinav Kumar,
• Brijesh Kumar,
• Vishnu K. Tandon and
• Vishnu Ji Ram

Beilstein J. Org. Chem. 2013, 9, 809–817, doi:10.3762/bjoc.9.92

• hydride-AIBN initiated radical cyclization [33][34]. In 2005, Player and co-workers reported a tandem Heck/Suzuki–Miyaura coupling process for the synthesis of (E)-3,3-(diaryl)oxindoles [35][36][37]. Recently, alkenylation of indolin-2-ones has been developed by palladium-catalyzed aromatic C–H activation

Recent advances in transition-metal-catalyzed intermolecular carbomagnesiation and carbozincation

• Kei Murakami and
• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 278–302, doi:10.3762/bjoc.9.34

• ]. As a result, Hoveyda’s zirconium-catalyzed reactions provided homobenzylmagnesium intermediates 4j, while Kambe’s titanium-catalyzed reactions afforded benzylmagnesium intermediates 4k. Kambe applied the titanocene-catalyzed reaction to a three-component coupling reaction involving a radical

• cyclization reaction (Scheme 44). Under Nakamura’s iron-catalyzed carbometalation reaction conditions (shown in Scheme 17), the reaction of oxabicyclic alkenes provided ring-opened product 4m through a carbomagnesiation/elimination pathway (Scheme 45, reaction 4l to 4m) [82]. In contrast, the use of the 1,2

Radical zinc-atom-transfer-based carbozincation of haloalkynes with dialkylzincs

• Fabrice Chemla,
• Florian Dulong,
• Franck Ferreira and
• Alejandro Pérez-Luna

Beilstein J. Org. Chem. 2013, 9, 236–245, doi:10.3762/bjoc.9.28

• alkyl iodides in the presence of Me2Zn/O2 with β-(propargyloxy)enoates entails the intramolecular carbometallation of the pendant alkynes substituted by silyl, alkyl, aryl, alkenyl or amino groups by a 5-exo dig radical cyclization step [37][38]. Intermolecular carbozincation of terminal arylacetylenes