[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• of 3-phenylsydnone and proposed formation of N-phenylnitrilimine as the main reaction product via an internal ring closure, extrusion of CO2 and ring opening (Scheme 6). This very reactive 1,3-dipole was trapped by reaction with external (14C-labelled) CO2 to give 3-phenyl-1,3,4-oxadiazol-2(3H)-one

An unusual thionyl chloride-promoted C−C bond formation to obtain 4,4'-bipyrazolones

• Gernot A. Eller,
• Gytė Vilkauskaitė,
• Algirdas Šačkus,
• Vytas Martynaitis,
• Ashenafi Damtew Mamuye,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2018, 14, 1287–1292, doi:10.3762/bjoc.14.110

• -substituents at the pyrazole C4 position, like 5-chloropyrazole-4-carbaldehydes or 4-esters, turned out to be particularly useful due to the easy conversion of the chloro substituent into other functional groups or its nature as a good leaving group in ring-closure reactions. In this respect we were interested

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

• compared by both experimental techniques and by means of MNDO calculations (Scheme 26) [131]. While the key steps for the thermal decomposition of tropones are electrocyclic ring closure and cheletropic CO extrusion to give an aromatic system, the cationic reactions occur with ring closure followed by the

Stepwise radical cation Diels–Alder reaction via multiple pathways

• Ryo Shimizu,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 704–708, doi:10.3762/bjoc.14.59

• rationalized that the six-membered ring closure of the acyclic radical cation intermediate (A·+) would be a stepwise process, leading to the Diels–Alder adduct 3 as an approximately cis/trans = 1:1 mixture. However, since the oxidative SET-triggered rearrangement of the vinylcyclobutane 4 gives the Diels–Alder

• adduct 3 as an approximately cis/trans = 1:4 mixture, this should proceed via a different intermediate from the acyclic radical cation intermediate (A·+). Here, we propose the cyclic radical cation intermediate B·+ for the rearrangement, imparting stereoselectivity for the six-membered ring closure. The

Continuous multistep synthesis of 2-(azidomethyl)oxazoles

• Thaís A. Rossa,
• Nícolas S. Suveges,
• Marcus M. Sá,
• David Cantillo and
• C. Oliver Kappe

Beilstein J. Org. Chem. 2018, 14, 506–514, doi:10.3762/bjoc.14.36

• preparation of oxazoles described in the literature. These include ring-closure reactions of diazocarbonyl compounds with amides or nitriles [16], α-haloketones and amides [17][18][19], cyanohydrins and aldehydes (Fischer synthesis) [20][21], or oxidative additions of α-methylene ketones to nitriles [22][23

From dipivaloylketene to tetraoxaadamantanes

• Gert Kollenz and
• Curt Wentrup

Beilstein J. Org. Chem. 2018, 14, 1–10, doi:10.3762/bjoc.14.1

• -type double bonds in the bisdioxines under acidic conditions generates a tertiary alcohol, which again undergoes a transannular oxa-Michael-type ring closure forming a tetraoxaadamantane. Free carboxylic acid functions are decarboxylated in this process (Scheme 7), but amide and ester functions are

• ) derived from dipivaloylketene (2). Mechanisms of formation of bisdioxine acid derivatives from dimer 3. Recently reported synthesis of chromenobisdioxines. Formation of tetraoxaadamantanes. Decarboxylative hydrolysis and oxa-Michael-type ring closure. Oxime and hydrazine derivatives of bisdioxines and

Vinylphosphonium and 2-aminovinylphosphonium salts – preparation and applications in organic synthesis

• Anna Kuźnik,
• Roman Mazurkiewicz and
• Beata Fryczkowska

Beilstein J. Org. Chem. 2017, 13, 2710–2738, doi:10.3762/bjoc.13.269

• to vinylphosphonium salt. A phosphorus ylide thus generated undergoes a subsequent intramolecular Wittig reaction, leading to a carbo- or heterocyclic ring closure (Scheme 2) [1][2][3]. This reaction can be considered as a general method for the synthesis of carbo- and heterocyclic systems

• subsequent 1,2-proton transfer followed by the elimination of triphenylphosphine and ring closure via formation of the new C–N bond gave the final γ-lactam derivatives 80 (Scheme 50) [66]. In 2013 Mohebat et al. used 6-amino-N,N'-dimethyluracil as an NH-acid and precursor of the carbon nucleophile in the

• carbonyl function to vinylphosphonium salts can be considered as a general method for a new ring closure to carbo- or heterocyclic systems of diversified size by the intramolecular Wittig reaction. Recently, significant attention attracts also highly reactive α,β-(dialkoxycarbonyl)vinylphosphonium salts

Ring-size-selective construction of fluorine-containing carbocycles via intramolecular iodoarylation of 1,1-difluoro-1-alkenes

• Takeshi Fujita,
• Ryo Kinoshita,
• Tsuyoshi Takanohashi,
• Naoto Suzuki and
• Junji Ichikawa

Beilstein J. Org. Chem. 2017, 13, 2682–2689, doi:10.3762/bjoc.13.266

• -difluoroallylic moiety, which might perturb cationic charge distribution in the corresponding cyclic iodonium intermediates. The aryl group in the 2-position (at the carbon atom in β-position to the fluorine substituents) promoted a six-membered-ring closure, most likely because of the localization of cationic

Preparation and isolation of isobenzofuran

• Morten K. Peters and
• Rainer Herges

Beilstein J. Org. Chem. 2017, 13, 2659–2662, doi:10.3762/bjoc.13.263

• phthalic acid (2) or phthalic acid ester 3 to 1,2-bis(hydroxymethyl)benzene (4) [19], acid promoted ring closure, and subsequent oxidation with hypochlorite in the presence of methanol gives 7 in a moderate yield of 65% [18]. Alternatively, phthalide 5 has been reduced to 1,3-dihydroisobenzofuran-1-ol (6

Recent progress in the racemic and enantioselective synthesis of monofluoroalkene-based dipeptide isosteres

• Myriam Drouin and
• Jean-François Paquin

Beilstein J. Org. Chem. 2017, 13, 2637–2658, doi:10.3762/bjoc.13.262

• fluorenylmethyloxycarbonyl group. Oxidation of the remaining alcohol to the corresponding carboxylic acid provided the dipeptide isostere 35. Couve-Bonnaire and co-workers developed the preparation of (E)-monofluoroalkene dipeptide isosteres towards an intramolecular ring-closure metathesis (Scheme 8) [35]. The bis-alkene

• 36 underwent a ring-closure metathesis reaction in the presence of catalyst 37 under microwave irradiation to give lactam 38. Deprotection of the amine followed by acidic opening of the ring gave the (E)-monofluoroalkene 39 in good yield. The reaction was also performed on the racemic starting

• the chiral sulfinylimine, reduction into the corresponding sulfinylamine using DIBAL, deprotection of the terminal alcohol and Mitsunobu ring closure into the corresponding pyrrolidine derivative. Then, simultaneous deprotection of the amine and the alcohol in acidic conditions followed by coupling

¹⁵N-Labelling and structure determination of adamantylated azolo-azines in solution

• Sergey L. Deev,
• Alexander S. Paramonov,
• Tatyana S. Shestakova,
• Igor A. Khalymbadzha,
• Oleg N. Chupakhin,
• Julia O. Subbotina,
• Oleg S. Eltsov,
• Pavel A. Slepukhin,
• Vladimir L. Rusinov,
• Alexander S. Arseniev and
• Zakhar O. Shenkarev

Beilstein J. Org. Chem. 2017, 13, 2535–2548, doi:10.3762/bjoc.13.250

• give [1,2-15N2]-tetrazolo[5,1-c][1,2,4]triazine 11-15N2. Indeed, [2,3-15N2]-tetrazolo[1,5-b][1,2,4]triazin-7-one 13-15N2 was obtained (see below). Most likely, tetrazole 11-15N2 underwent a ring-opening process, yielding azide 12-15N2, and this process was followed by an alternative ring closure. This

Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines

• Elisandra Scapin,
• Paulo R. S. Salbego,
• Caroline R. Bender,
• Alexandre R. Meyer,
• Anderson B. Pagliari,
• Tainára Orlando,
• Geórgia C. Zimmer,
• Clarissa P. Frizzo,
• Helio G. Bonacorso,
• Nilo Zanatta and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 2396–2407, doi:10.3762/bjoc.13.237

• determine that over 90% of the mixture is in the form of 2-azidopyrimidine 4d in CDCl3. This proves the effect of the solvent in the tetrazolo[1,5-a]pyrimidine2-azidopyrimidine equilibrium. The highly polar DMSO-d6 favors the ring closure to form tetrazolo[1,5-a]pyrimidines in larger quantities (3d:4d in a

• nitrogen atom next to the methyl group participates in the ring closure. This equilibrium was not observed in the other compounds addressed in this work. In general, tetrazolo[1,5-a]pyrimidines with 7-CF3 or 7-CCl3 substituents were observed in DMSO-d6 or CDCl3, while 2-azidopyrimidine was found in the

Synthesis and photophysical properties of novel benzophospholo[3,2-b]indole derivatives

• Mio Matsumura,
• Mizuki Yamada,
• Atsuya Muranaka,
• Misae Kanai,
• Naoki Kakusawa,
• Daisuke Hashizume,
• Masanobu Uchiyama and
• Shuji Yasuike

Beilstein J. Org. Chem. 2017, 13, 2304–2309, doi:10.3762/bjoc.13.226

• Scheme 1. The key precursor 2 was synthesized by I2-mediated electrophilic cyclization of 2-ethynyl-N,N-dimethylaniline 1 [36][37]. Treatment of compound 2 with n-butyllithium in anhydrous THF at −78 °C and subsequently with PhPCl2 resulted in ring closure, affording the desired benzophospholo[3,2-b

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• first one is the ring closure leading to 9, and the second one involves the addition of a second carbene followed by ring closure to yield 8. The reaction with Z-1b led to the same set of products with trans-orientation of the substituents in 8 indicating the appearance of an intermediate zwitterion 11

• ] (Scheme 26). The formation of the products is initiated by the nucleophilic attack of either C4 or NH2 of 81 onto E-1, followed, in both cases, by elimination of HCN to give intermediates 84 and 85, respectively. The heterocyclization leading to 82 is a lactamization, whereas a ring closure via N attack

• succinate 91 (see chapter Michael type reactions) [54] (Scheme 28). In this case, the reaction pathway comprises the ring closure through the attack of the O-nucleophile onto the terminal cyano group. The analogous reaction was reported for the enolizable indane-1,3-dione. Redox reactions The replacement of

Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz–Fritsch–Bobbitt reaction with non-activated and moderately-activated systems

• Marco Mottinelli,
• Mathew P. Leese and
• Barry V. L. Potter

Beilstein J. Org. Chem. 2017, 13, 1871–1878, doi:10.3762/bjoc.13.182

• -ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO4

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

• principal approaches have been used to establish the 12-membered macrolactone ring, namely (1) ring-closure by macrolactonization, the approach followed by Kishi, Negishi and Aggarwal, or (2) ring-closing olefin metathesis (RCM) to form the C8–C9 double bond, which is part of Burkart’s and Altmann’s

Direct catalytic arylation of heteroarenes with meso-bromophenyl-substituted porphyrins

• Alexei N. Kiselev,
• Olga K. Grigorova,
• Alexei D. Averin,
• Sergei A. Syrbu,
• Oskar I. Koifman and
• Irina P. Beletskaya

Beilstein J. Org. Chem. 2017, 13, 1524–1532, doi:10.3762/bjoc.13.152

• isocyanide Pd complex followed by the ring closure [32]; on the other hand, the arylation of benzothiophene in the presence of Pd(OAc)2/PCy3*HBF4/PivOH proceeds in accordance with the concerted metalation–deprotonation mechanism [33][34]. We also investigated the reaction of zinc meso-(3-bromophenyl

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• -assisted ring closure of the corresponding aminoamides promoted by ethyl polyphosphate (PPE). Keywords: dihydroquinazolines; microwaves; N-acylations; N-alkylations; PPE; Introduction Nitrogen heterocycles are part of many drugs and represent structures with wide therapeutic potential. Therefore, much

• microwave irradiation at 110 ºC for 4 minutes. Due to the easier preparation and the inexpensive reagents required for its synthesis [65], PPE was chosen as cyclodehydrating agent for the preparation of compounds 1. Results and optimized experimental conditions of the MW-assisted ring-closure reaction are

• nucleus almost unexplored. To our knowledge, this is the first general method available for synthesis of these compounds. The products were synthesized by microwave-assisted ring closure of different aminoamides promoted by PPE. The yields and reaction times involved in the heterocyclization step compare

A new member of the fusaricidin family – structure elucidation and synthesis of fusaricidin E

• Marcel Reimann,
• Louis P. Sandjo,
• Luis Antelo,
• Eckhard Thines,
• Isabella Siepe and
• Till Opatz

Beilstein J. Org. Chem. 2017, 13, 1430–1438, doi:10.3762/bjoc.13.140

• natural fusaricidin by the Jolliffe group employed a ring closure via a lactonization in solution and subsequent attachment of the side chain to the cyclized depsipeptide [10]. Since the macrolactonization approach suffered from diastereoselectivity issues and low yield, it was decided to perform an on

Total syntheses of the archazolids: an emerging class of novel anticancer drugs

• Stephan Scheeff and
• Dirk Menche

Beilstein J. Org. Chem. 2017, 13, 1085–1098, doi:10.3762/bjoc.13.108

• C10 and C12. Based on this analysis, their synthetic plan was to first build the triene, while the C2–C5 fragment should be constructed directly before or during ring closure as shown in Scheme 2. Consequently, they first planned to connect the north-eastern fragment 5 with the propionate unit 4 by a

A strategic approach to [6,6]-bicyclic lactones: application towards the CD fragment of DHβE

• Tue Heesgaard Jepsen,
• Emil Glibstrup,
• François Crestey,
• Anders A. Jensen and
• Jesper Langgaard Kristensen

Beilstein J. Org. Chem. 2017, 13, 988–994, doi:10.3762/bjoc.13.98

• hydrolysis of the Cbz group to some extent. The final ring-closure to the CD-ring fragment 20 was successfully achieved with 31% yield over 3 steps. Only the desired (E)-6-exo 18 isomer reacted, leaving the (Z)-exo isomer 19 uncyclized, as anticipated. Inspired by the successful Cbz deprotection of a very

New approach toward the synthesis of deuterated pyrazolo[1,5-a]pyridines and 1,2,4-triazolo[1,5-a]pyridines

• Aleksey Yu. Vorob’ev,
• Vyacheslav I. Supranovich,
• Gennady I. Borodkin and
• Vyacheslav G. Shubin

Beilstein J. Org. Chem. 2017, 13, 800–805, doi:10.3762/bjoc.13.80

• intramolecular ring closure [21][22][23][24]. The importance of these cores for medical chemistry studies suggests that isotopically labeled pyrazolo[1,5-a]pyridines and triazolo[1,5-a]pyridines could be of interest. Recently, deuterium-labeled pyridinium-N-imines were applied to mechanistic studies of the

Phosphazene-catalyzed desymmetrization of cyclohexadienones by dithiane addition

• Matthew A. Horwitz,
• Elisabetta Massolo and
• Jeffrey S. Johnson

Beilstein J. Org. Chem. 2017, 13, 762–767, doi:10.3762/bjoc.13.75

• phosphazene bases in deprotonating carboxylate dithianes, we selected the commercially available achiral superbase P2-t-Bu phosphazene to initiate the ring closure (Scheme 2) [31][32]. We found that in the simplest case, with the methyl-substituted para-quinol ester (1a), the reaction was complete in 30 min

N-Propargylamines: versatile building blocks in the construction of thiazole cores

• S. Arshadi,
• E. Vessally,
• L. Edjlali,
• R. Hosseinzadeh-Khanmiri and
• E. Ghorbani-Kalhor

Beilstein J. Org. Chem. 2017, 13, 625–638, doi:10.3762/bjoc.13.61

• reaction is based on the formation of β-oxo-N-propargyl thioamides A as intermediates, followed by their spontaneous ring closure. This reaction was run in refluxing ethanol and provided in all cases the desired thiazolidines 42 in high to excellent yields (Scheme 10) [93]. In 2009, Yarovenko and co

Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• yields of up to 74% and trace amounts of the auto-condensation products 6 (Scheme 3). Even in the deactivated derivatives containing halogen atoms at the aromatic system, the cyclopentanone ring closure took place quite easily [14]. If other Lewis acids, such as Bi(NTf2)3 or triflate derivatives of the

• 76% yield. The former 271 was obtained from the trienone 270/270’ which underwent ring closure to give the 6-membered ring [105] (Scheme 76). 2.2 From alkynes DBU and CpRu(PPh3)2Cl dual catalysts enabled a one-pot annulation of aldehyde 273 and cyclopentanone (274) to give the 1-indanone derivative