Mechanism, kinetics and selectivity of selenocyclization of 5-alkenylhydantoins: an experimental and computational study

• Biljana M. Šmit,
• Radoslav Z. Pavlović,
• Dejan A. Milenković and
• Zoran S. Marković

Beilstein J. Org. Chem. 2015, 11, 1865–1875, doi:10.3762/bjoc.11.200

• -membered ((S,R)-INT3 and (S,S)-INT3) or six-membered ((S,R)-INT3’ and (S,S)-INT3’) intermediate bicyclic imidazolinium cations. Energy profiles for both 5-exo and 6-endo pathways are presented in Figure 3. The ring closure reactions are carried out via four transition states: two for the formation of the

• and susceptible to the nucleophilic attack of N(1) atom. Subsequent ring closure is the rate-determing step and also the step in which the cyclization mode and distribution of the products is determined (Figure 3). This process was followed in 1H NMR experiments by the increase of the signal

• intermediate imidazolinium cations. The last step of the reaction is deprotonation followed by the formation of the fused bicyclic hydantoins. DFT calculations support a plausible reaction pathway where the ring closure is the rate-determining step. The preferred 5-exo cyclization is confirmed. Elucidation of

Recent applications of ring-rearrangement metathesis in organic synthesis

• Sambasivarao Kotha,
• Milind Meshram,
• Priti Khedkar,
• Shaibal Banerjee and
• Deepak Deodhar

Beilstein J. Org. Chem. 2015, 11, 1833–1864, doi:10.3762/bjoc.11.199

• : a sequential aldol condensation of dihydrocarvone with norbornene 2-carboxaldehyde followed by a ROM–RCM of the resulting aldol product. The norbornene derivative 164 was subjected to a RRM using the catalyst 1 to produce the ROM product 165 exclusively. The ring-closure of the resulting ROM product

SmI₂-mediated dimerization of indolylbutenones and synthesis of the myxobacterial natural product indiacen B

• Nils Marsch,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2015, 11, 1700–1706, doi:10.3762/bjoc.11.184

• ][28]. Thus, the indole NH group (pKa about 21 in DMSO) should be able to serve as a stoichiometric proton source that, after β,β'-coupling, would convert one of the Sm(III) enolates to the ketone. Attack of the remaining Sm(III) enolate would lead to Dieckmann-type ring closure, followed by

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

• converted into an amide in the presence of methylaminoacetaldehyde dimethylacetal. A ring closure occurs by treating the amide with a strong acid. The reaction gave a mixture of a quinone and a dimethoxy intermediate that were first reduced to amine products. Furthermore, the dimethoxy intermediate was

A facile synthetic route to benzimidazolium salts bearing bulky aromatic N-substituents

• Gabriele Grieco,
• Olivier Blacque and
• Heinz Berke

Beilstein J. Org. Chem. 2015, 11, 1656–1666, doi:10.3762/bjoc.11.182

• -step synthesis avoiding chromatographic work-up. In the key step triethyl orthoformate is reacted with the corresponding N1,N2-diarylbenzene-1,2-diamines and then further transformed in situ, by alkoxy abstraction using trimethylsilyl chloride (TMSCl), and concomitant imidazole ring closure. Keywords

• of nucleophilic aromatic substitutions (SNAr) of benzene-1,2-diamine at 2-chloropyridine (Scheme 1). Once all the different N1,N2-diarylbenzene-1,2-diamines were prepared a method had to be developed to build up the imidazolium salts by ring closure. 3-Cl and 4-Cl could principally be obtained from

• stability of the [BF4]− anion could lead to complications generating side-products [50][51][52]. The preparations of both 3-Cl and 4-Cl started along the given lines with the syntheses of the respective aryl-substituted diamines, which had to undergo ring closure in the presence of a C1 component. For 3-Cl

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• in an aqueous dispersion of a Pt-TiO2 catalyst, an interesting self-reaction occurred. Ohtani and co-workers isolated modest yields of secondary amines 13 that were formed via C–N coupling (Scheme 4, top) [48]. Terminal diamines reacted by ring closure resulting in cyclic amines 14; pyrrolidine was

Towards inhibitors of glycosyltransferases: A novel approach to the synthesis of 3-acetamido-3-deoxy-D-psicofuranose derivatives

• Maroš Bella,
• Miroslav Koóš and
• Chun-Hung Lin

Beilstein J. Org. Chem. 2015, 11, 1547–1552, doi:10.3762/bjoc.11.170

• -acetamido-3-deoxy-α-D-psicofuranose 11 resulted in ring closure of the acetamido group, affording 2-methyloxazoline derivatives 13 and 14. Further research into an alternative strategy for the synthesis of 3-azido-3-deoxy-D-psicofuranose derivatives will be performed so as to avoid the formation of the 2

Cross-metathesis reaction of α- and β-vinyl C-glycosides with alkenes

• Ivan Šnajdr,
• Kamil Parkan,
• Filip Hessler and
• Martin Kotora

Beilstein J. Org. Chem. 2015, 11, 1392–1397, doi:10.3762/bjoc.11.150

• vinyl β-C-deoxyribofuranoside was based on transformation of 6-O-tert-butyldiphenylsilyl-3,5-dideoxy-5-iodo-L-lyxo-hexofuranose [14]. A reaction sequence relying on Horner–Wadsworth–Emmons/ring closure–halogenation/Ramberg–Bäcklund/Wittig reaction gave rise to the equimolar mixture of styryl α- and β-C

Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• CO2, catalysed by LiBr [41]. The preferred pathways principally involve ring opening of the epoxide, followed by CO2 insertion and ring closure of the cyclic carbonate. Interestingly, in the Re(I)-catalysed reaction (b), an alternative reaction pathway was followed, whereby the first step is CO2

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

Novel carbocationic rearrangements of 1-styrylpropargyl alcohols

• Christine Basmadjian,
• Fan Zhang and
• Laurent Désaubry

Beilstein J. Org. Chem. 2015, 11, 1017–1022, doi:10.3762/bjoc.11.114

• formation of the stabilized carbocation 11 that may evolve through two pathways. This intermediate may either undergo a ring closure due to the nucleophilic character of the silylated alkyne (pathway A) or react with an oxygenated nucleophile, such as the perrhenate anion, to generate the transient

Novel stereocontrolled syntheses of tashiromine and epitashiromine

• Loránd Kiss,
• Enikő Forró and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2015, 11, 596–603, doi:10.3762/bjoc.11.66

• stereocontrolled approach has been developed for the syntheses of tashiromine and epitashiromine alkaloids from cyclooctene β-amino acids. The synthetic concept is based on the azetidinone opening of a bicyclic β-lactam, followed by oxidative ring opening through ring C–C double bond and reductive ring-closure

• reactions of the cis- or trans-cyclooctene β-amino acids. Keywords: alkaloids; amino acids; ring closure; ring opening; stereocontrolled synthesis; Introduction Indolizidine alkaloids are an important class of naturally occurring compounds which have received considerable attention as a result of their

• the indolizidine framework; access to tashiromine in racemic form can be achieved through the alkylation of succinimide, followed by ring closure via acyliminium intermediates [23][24], the reduction of cyclized pyridinium salts [25], iminium cascade cyclization [26], alkyne-mediated hydroformylation

Metal-free one-pot synthesis of 2-substituted and 2,3-disubstituted morpholines from aziridines

• Hongnan Sun,
• Binbin Huang,
• Run Lin,
• Chao Yang and
• Wujiong Xia

Beilstein J. Org. Chem. 2015, 11, 524–529, doi:10.3762/bjoc.11.59

• haloalkoxy amine intermediate 2a after abstraction of one hydrogen atom from alcohol. Finally, an intramolecular ring closure affords the morpholine product 3a in the presence of KOH [21]. Conclusion In conclusion, we have developed a simple and practicable metal-free protocol for the synthesis of 2

The preparation of new functionalized [2.2]paracyclophane derivatives with N-containing functional groups

• Henning Hopf,
• Swaminathan Vijay Narayanan and
• Peter G. Jones

Beilstein J. Org. Chem. 2015, 11, 437–445, doi:10.3762/bjoc.11.50

• bridging and the strain of the desired 17 would be too high for a successful ring closure. Reacting 16 with tetraethylene glycol (TEG) under high dilution conditions (toluene, reflux, 7 d) provides the crownophane 18 in 68% yield (Scheme 2). Likewise, replacement of TEG by pentaethylene glycol (PEG

Bis(vinylenedithio)tetrathiafulvalene analogues of BEDT-TTF

• Erdal Ertas,
• İlknur Demirtas and
• Turan Ozturk

Beilstein J. Org. Chem. 2015, 11, 403–415, doi:10.3762/bjoc.11.46

• molecules, obtained from 1,8-diketone ring closure reactions, and coupling reactions, published by our group. Review BVDT-TTF analogues from 1,8-diketones Bis(vinylenedithio)tetrathiafulvalene (BVDT-TTF) 4 (R = Ph, 4-CH3OC6H4, 4-BrC6H4, 4-CH3C6H4, 4-O2NC6H4, 2-thienyl) is a fully unsaturated analogue of

• temperature for 3 h in 90% yield (Scheme 6) [40]. The ring closure reaction of 47 was performed initially using LR, which produced only the thiophene 50, similar to the result obtained by another research group [28]. Next, the reaction was conducted with P4S10, which gave benzylphenyldithiole 49 and the

• reported in 2013 [58]. Their syntheses began with our standard synthesis of a 1,8-diketone 74 having a thiophene in place of a benzenoid aromatic group (Scheme 11). Reaction of the zinc-complex 59 with four mol equivalents of α-bromoketone 72 gave the diketone 74 in 80% yield, subsequent ring closure of

Synthesis of the furo[2,3-b]chromene ring system of hyperaspindols A and B

• Danielle L. Paterson and
• David Barker

Beilstein J. Org. Chem. 2015, 11, 265–270, doi:10.3762/bjoc.11.29

• reversibility of the ring closure and preferred formation of isomer 7a. Conclusion In conclusion, the first synthesis of the furo[2,3-b]chromene ring system found in hyperaspidinols A (1) and B (2) has been achieved. Analysis of the NMR of synthetic furo[2,3-b]chromenes 7a and 7b and comparison to the data of 1

A facile synthesis of functionalized 7,8-diaza[5]helicenes through an oxidative ring-closure of 1,1’-binaphthalene-2,2’-diamines (BINAMs)

• Youhei Takeda,
• Masato Okazaki,
• Yoshiaki Maruoka and
• Satoshi Minakata

Beilstein J. Org. Chem. 2015, 11, 9–15, doi:10.3762/bjoc.11.2

• ) reductive ring-closure of 2,2’-dinitro-1,1’-binaphthalenes using various reductants such as Na2S and LiAlH4 [20][21], and iii) the Scholl-type cyclization of 2,2’-azonaphthalenes using a eutectic melt of AlCl3/NaCl [22]. However, these methods require harsh reaction conditions such as the use of strong

• diazahelicenes though. Another simple synthetic route to 7,8-diaza[5]helicenes would involve an oxidative ring-closure of 1,1’-binaphthalene-2,2’-diamines (BINAMs) (Scheme 1, iv). However, interestingly enough, this route remains to be explored. Corbett and Holt reported that the oxidation of BINAM with NaBO3

• . Herein we present a facile, straightforward, and moderately functional-group-tolerant synthesis of 7,8-diaza[5]helicenes (benzo[f]naphtho[2,1-c]cinnolines) bearing functional substituents on the helical π-conjugated backbone through an oxidative ring-closure of BINAM derivatives (Scheme 2, the lower

Enantioselective synthesis of polyhydroxyindolizidinone and quinolizidinone derivatives from a common precursor

• Nemai Saha and
• Shital K. Chattopadhyay

Beilstein J. Org. Chem. 2014, 10, 3104–3110, doi:10.3762/bjoc.10.327

• unsaturated amide 9 in readiness for a subsequent RCM reaction. Ring closure of 9 proceeded better in the presence of Grubbs’ second generation catalyst [34] to provide the indolizidine derivative 10 in good yield. Similarly, treatment of amine 8 with vinylacetic acid in the presence of EDC/HOBt under

• standard conditions proceeded smoothly to provide the N-tethered diene 11. Ring-closure of compound 11 proved to be more facile, as expected, and the quinolizidine derivative 12 was obtained in higher yield. The four step sequences 6→10 and 6→12 proceeded in overall yields of 56% and 67%, respectively

A one-pot multistep cyclization yielding thiadiazoloimidazole derivatives

• Debabrata Samanta,
• Anup Rana,
• Jan W. Bats and
• Michael Schmittel

Beilstein J. Org. Chem. 2014, 10, 2989–2996, doi:10.3762/bjoc.10.317

• intramolecular nucleophilic attack at its central, highly electrophilic carbon by the adjacent -NH- of the yet unreacted thiourea unit to produce 4 in a first cyclization step (cyclization-I). The second ring closure to generate the 1,2,4-thiadiazole ring may be assisted by one equivalent of methansulfonyl

• energies of the ring closure steps according to our mechanistic hypothesis were computed and found to comply with a facile reaction at room temperature. Experimental General methods. All reagents were utilized as received from commercial suppliers. NMR spectra, infrared spectra, elemental analysis and

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

• pyrolysis of the condensation product of benzaldehyde and aniline [6]. The reaction conditions were improved by Morgan and Walls, based on a reaction including a cyclization of phenanthridine by dehydrative ring-closure with phosphorus oxychloride in boiling nitrobenzene [7]. Over the 20th century this

• various substituents, which were nicely summarized by Keller a decade ago [8]. We tried to survey the wide range of synthetic methods applied from 2000 on organizing them by similarity of reactants/catalysts or organic reactions; for instance the anionic ring-closure reactions using Grignard reagents

• diarylmethanes, acridine, xanthene, thioxanthene, etc. It was based on the generation of a benzotriazole-stabilized carbanion followed by oxidation of this carbanion by copper iodide to form a radical. Subsequent elimination of nitrogen followed by ring closure yielded phenanthridine (Scheme 2) [13][14]. In the

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

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

• 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

• . Intermolecular cyclizations generally fall into two further categories. In the first scenario, an anodically generated nucleophile (cathodically generated electrophile) reacts with an electrophile (nucleophile) present in solution. Consequently, an intermediate is formed, which undergoes ring-closure reaction

• Michael addition/ring closure with in situ generated quinones (section 2.2) and sequential cyclizations involving acyliminium species and alkoxycarbenium ions (section 2.3) represent the majority of recently reported intermolecular electrochemical cyclizations. Cases which do not fall into any of these

Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction

• László Tóth,
• Yan Fu,
• Hai Yan Zhang,
• Attila Mándi,
• Katalin E. Kövér,
• Tünde-Zita Illyés,
• Attila Kiss-Szikszai,
• Balázs Balogh,
• Tibor Kurtán,
• Sándor Antus and
• Péter Mátyus

Beilstein J. Org. Chem. 2014, 10, 2594–2602, doi:10.3762/bjoc.10.272

• neuroprotective condensed 2-phenyl-1,4-benzoxazepines rac-7a,b through the diastereoselective domino Knoevenagel–1,5-hydride shift cyclization reaction rac-5→rac-7a,b from the readily available 4-aryl-2-phenyl-1,4-benzoxazepine derivative, rac-5 (Scheme 1). Ring-closure transformations involving C(sp3)–H bond

New highlights of the syntheses of pyrrolo[1,2-a]quinoxalin-4-ones

• Emilian Georgescu,
• Alina Nicolescu,
• Florentina Georgescu,
• Florina Teodorescu,
• Daniela Marinescu,
• Ana-Maria Macsim and
• Calin Deleanu

Beilstein J. Org. Chem. 2014, 10, 2377–2387, doi:10.3762/bjoc.10.248

• imidazole ring-opening, initiated by the deprotonation at C-1 of the primary cycloadducts 8, followed by ring-closure involving the carbethoxy C=O group, a previously proposed rationale [9]. The formation of pyrrolo[1,2-a]benzimidazoles 5 involves the spontaneous in situ dehydrogenation of the primary

Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

• Ivana Šagud,
• Simona Božić,
• Željko Marinić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230

• formation of the photoproducts 8 and 10 can be explained by intramolecular cycloaddition and formation of resonance stabilized biradicals A/A’ followed by the 1,6-ring closure (Scheme 4). An 1,3-H shift, as in furan and thiophene derivatives [6], and rearomatization to fused oxazole derivatives B/B’ is not

• detected. The 1,6-ring closure of the biradicals A/A’ occurs stereoselectively giving the major products rel-(2S)-8a/rel-(2S)-10 in which the hydrogen on C-2 is oriented toward the methano bridge. The formation of dihydronaphthalene derivative 9, found only on irradiation of 1, is explained by 6π

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

• Thilo Focken and
• Stephen Hanessian

Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195