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

• reported 4,5-benzotropolone 238 and its methyl ether do not give the characteristic aromatization reactions as colchicine and monocyclic tropolones, and explained that 238 is a weaker acid than colchicine or tropolone [157]. However, the conversion of 238 to 1-nitro-2-naphthoic acid (259) was reported in

An efficient and facile access to highly functionalized pyrrole derivatives

• Meng Gao,
• Wenting Zhao,
• Hongyi Zhao,
• Ziyun Lin,
• Dongfeng Zhang and
• Haihong Huang

Beilstein J. Org. Chem. 2018, 14, 884–890, doi:10.3762/bjoc.14.75

• cycloadduct 11a to pyrrolo[3,4-c]pyrrole-1,3-dione 12a was investigated (Table 3). For the operational simplicity and continuity of this one-pot condensation–cycloaddition–aromatization reaction, CH2Cl2 was firstly selected as solvent instead of the generally used toluene [10][25][26] for this oxidation step

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• and the aldehyde yields a Schiff base and then the latter reacts with 2-naphthol in the second nucleophilic addition step. The other theory assumes the formation of an ortho-quinone methide (o-QM) intermediate by the reaction of 2-naphthol and benzaldehyde. Re-aromatization, the driving force of the

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• , dehydration and aromatization reactions. The use of ionic liquids (non-volatile solvents) over toxic organic solvents makes it an environmentally benign process [45][46]. The synthesis of isomeric tetracyclic pyrazolo[3,4-b]pyridine-based coumarin chromophores 27 and 28 was reported by Chen et al. [47

Aminomethylation/hydrogenolysis as an alternative to direct methylation of metalated isoquinolines – a novel total synthesis of the alkaloid 7-hydroxy-6-methoxy-1-methylisoquinoline

• Benedikt C. Melzer,
• Jan G. Felber and
• Franz Bracher

Beilstein J. Org. Chem. 2018, 14, 130–134, doi:10.3762/bjoc.14.8

• starting aldehyde 2 was subjected to a reductive amination with aminoacetaldehyde dimethyl acetal and NaBH4, followed by N-tosylation and hydrochloric acid-mediated cyclization under concomitant N-detosylation and aromatization. Direct ring metalation of 3 with TMPMgCl∙LiCl was performed as described by us

Oxidative dehydrogenation of C–C and C–N bonds: A convenient approach to access diverse (dihydro)heteroaromatic compounds

• Santanu Hati,
• Ulrike Holzgrabe and
• Subhabrata Sen

Beilstein J. Org. Chem. 2017, 13, 1670–1692, doi:10.3762/bjoc.13.162

• reactions are one of the key synthetic strategies that are applied to generate various nitrogen heterocycles and subsequent aromatization of these heterocycles afforded the corresponding heteroaromatic derivatives [19]. The aromatization of nitrogen heterocycles is facilitated mainly by dehydrogenation of

• at times lead to complete aromatization of the moiety based on the dehydrogenation capability of the oxidant as well as the presence of the appropriate acidic protons in the heterocyclic substrate (path b', Scheme 1). To attend greener synthesis metal catalyzed and organocatalytic aerobic oxidative

• and when 40b was reacted with 2 equivalents of the same reagent, it afforded 41. The ester functionality on 40b facilitated the complete aromatization of the ring to afford the desired products (Scheme 11). It is always a tedious effort to activate a sp3 C–H bond towards any transformation. A method

Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

• Stephen Hill and
• M. Carmen Galan

Beilstein J. Org. Chem. 2017, 13, 675–693, doi:10.3762/bjoc.13.67

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

• ) followed by the oxidative aromatization with Pd/C (Scheme 67). The latter was further used as a substrate for the synthesis of bisoxazolidine ligand 242. The same Diels–Alder reaction to obtain 241 has been used by Katsumura et al. [97]. In this case, 241 was further converted to cis-1-amino-7-methyl-2

• treatment with p-toluenesulfonic acid in acetone to give the diketone 245 (Scheme 68). Then, the latter underwent oxidative aromatization by treatment with Pd/C in p-cymene. The synthesized 1-indanone 246 was further converted to the cis-1-amino-2-indanol 247 and used as ligand for asymmetric reactions. A

• phenylselenyl-substituted cyclopentenone 269 was less effective and gave 1-indanone 265 in 28% yield only (Scheme 75) [102]. Another example of this reaction catalyzed by a Lewis acid has also been reported [104]. The flash vacuum pyrolysis has been applied for aromatization of 271 to afford 1-indanone 272 in

Regiochemistry of cyclocondensation reactions in the synthesis of polyazaheterocycles

• Patrick T. Campos,
• Leticia V. Rodrigues,
• Andrei L. Belladona,
• Caroline R. Bender,
• Juliana S. Bitencurt,
• Fernanda A. Rosa,
• Davi F. Back,
• Helio G. Bonacorso,
• Nilo Zanatta,
• Clarissa P. Frizzo and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 257–266, doi:10.3762/bjoc.13.29

• , followed by aromatization finally generates product 5 (Scheme 1). The trichloromethyl (CCl3) substituent as a leaving group in β-alkoxyvinyl trichloromethyl ketones has been previously used by us for the synthesis of similar heterocycles [27][28]. Products 5–7 are considered to be very attractive building

cis-Diastereoselective synthesis of chroman-fused tetralins as B-ring-modified analogues of brazilin

• Dimpee Gogoi,
• Runjun Devi,
• Pallab Pahari,
• Bipul Sarma and
• Sajal Kumar Das

Beilstein J. Org. Chem. 2016, 12, 2816–2822, doi:10.3762/bjoc.12.280

• group of 5 and/or 9, leading to the formation of a stable 3°carbocation that can undergo further dehydration reactions until full aromatization to the naphthalene ring is achieved. This study would serve to help us to find the real scenario. Finally, in the presence of Lewis/Brønsted acids, substrates 6

Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides

• Ilya V. Efimov,
• Marsel Z. Shafikov,
• Nikolai A. Beliaev,
• Natalia N. Volkova,
• Tetyana V. Beryozkina,
• Wim Dehaen,
• Zhijin Fan,
• Viktoria V. Grishko,
• Gert Lubec,
• Pavel A. Slepukhin and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2016, 12, 2390–2401, doi:10.3762/bjoc.12.233

• in good yields (Scheme 2). Probably the formation of nitrile oxides from hydroxamoyl chlorides occurs catalytically due to formation of dimethylamine as a result of the aromatization reaction with the isoxazoles, in which dimethylamine is formed. One can also propose that enamines 1 or traces of

A convenient route to symmetrically and unsymmetrically substituted 3,5-diaryl-2,4,6-trimethylpyridines via Suzuki–Miyaura cross-coupling reaction

• Dariusz Błachut,
• Joanna Szawkało and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2016, 12, 835–845, doi:10.3762/bjoc.12.82

• or pyrimidines with subsequent aromatization of the heterocyclic ring. We also noticed that the final composition of these markers was dependent on the reaction conditions during the drug synthesis [24]. In order to unequivocally confirm the presence of newly identified markers in the reaction

Biosynthesis of α-pyrones

• Till F. Schäberle

Beilstein J. Org. Chem. 2016, 12, 571–588, doi:10.3762/bjoc.12.56

• biosynthesis via norlichexanthone was ruled out by incorporation studies in Alternaria tenuis using [1-13C, 18O2]-labeled acetate. This resulted in high incorporation of acetate-derived oxygen into all the oxygen-bearing carbons [76]. A proposed biosynthetic pathway of 17 [77] (by aromatization of a polyketide

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

• concerted β-elimination along a C–C single bond), with the concomitant aromatization of the central ring. The computed energy barriers for these concerted β-eliminations are high, 41.7 and 40.8 kcal·mol−1 respectively [50]. Concerning the alternative reaction paths B and C, we have located essentially the

Photoinduced 1,2,3,4-tetrahydropyridine ring conversions

• Baiba Turovska,
• Henning Lund,
• Viesturs Lūsis,
• Anna Lielpētere,
• Edvards Liepiņš,
• Sergejs Beljakovs,
• Inguna Goba and
• Jānis Stradiņš

Beilstein J. Org. Chem. 2015, 11, 2166–2170, doi:10.3762/bjoc.11.234

• functional group is placed near to electronegative groups, the oxidizing capability of hydroperoxides can be increased. This effect was particularly observed on heterocyclic systems. Results and Discussion Photosensitized aerobic oxidative aromatization [11][12][13][14] of Hantzsch 1,4-dihydropyridines has

A convenient four-component one-pot strategy toward the synthesis of pyrazolo[3,4-d]pyrimidines

• Mingxing Liu,
• Jiarong Li,
• Hongxin Chai,
• Kai Zhang,
• Deli Yang,
• Qi Zhang and
• Daxin Shi

Beilstein J. Org. Chem. 2015, 11, 2125–2131, doi:10.3762/bjoc.11.229

• results in hand, two possible reaction mechanisms were proposed and shown in Scheme 3. 5-Aminopyrazole-4-carbonitrile 6 was obtained from the reaction of hydrazine 1 and methylenemalononitrile 2 through nucleophilic addition, cyclization and aromatization. The nucleophilic attack of the amino group of 6

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

• required RRM product 208 was formed in 26% yield. Later, the expected chiral buckybowl 209 was assembled via aromatization of 208 in the presence of DDQ (Scheme 42). Design of intricate polyquinanes has been considered as a challenging task for synthetic chemists. To this end, Fallis and co-workers [46

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

• imine formation and aromatization, occurred presumably due to the presence of an acidic solvent. Styelsamine B (4) was obtained with an overall yield of 35%. This pyridinium salt was treated with an ampholyte to afford its neutral form cystodytin J (Scheme 1) [58]. This biomimetic synthetic strategy is

Tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds

• Javier Miró,
• María Sánchez-Roselló,
• Álvaro Sanz,
• Fernando Rabasa,
• Carlos del Pozo and
• Santos Fustero

Beilstein J. Org. Chem. 2015, 11, 1486–1493, doi:10.3762/bjoc.11.161

• -Diels–Alder reaction involving alkynes, ethyl glyoxalate and ethyl vinyl ether was described for the preparation of 2,3-dihydropyrans [24][25]. Additionally, a tandem CEYM–IMDAR reaction in combination with a final aromatization step was employed for the synthesis of biaryl derivatives [26]. Herein, a

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

• different dienophiles followed by aromatization which gave the crownophanes (e.g., 148 and 151) (Scheme 22). Cross metathesis: In 1992, (−)-cylindrocyclophane A (156) and (−)-cylindrocyclophane F (155) were isolated by Moore and co-workers [143] from a blue-green algae belonging to Cylindrospermum

• -unsaturated ketone delivered the compound 169 (64%). Finally, aromatization of compound 169 by using potassium 3-aminopropylamide (KAPA) gave compound 170 (75%) (Scheme 26). Ring-closing metathesis (RCM): In 2003, Tae and Yang [152] have reported an efficient macrocyclization of various alkenyl derivatives

• acetylenedicarboxylate (DMAD) to deliver compounds 332a,b (77%). These DA adducts were irradiated in diethyl ether/dichloromethane (5:1) to offer the corresponding bioxaquadricyclane 333, subsequent thermolysis gave the bioxepine 334 (81%). Finally, aromatization of bioxepine 334 with trifluoroacetic acid (TFA

Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F₄TCNQ

• Raúl García,
• M. Ángeles Herranz,
• Edmund Leary,
• M. Teresa González,
• Gabino Rubio Bollinger,
• Marius Bürkle,
• Linda A. Zotti,
• Yoshihiro Asai,
• Fabian Pauly,
• Juan Carlos Cuevas,
• Nicolás Agraït and
• Nazario Martín

Beilstein J. Org. Chem. 2015, 11, 1068–1078, doi:10.3762/bjoc.11.120

• study by Hong et al., a conductance peak was found at log(G/G0) = −4.5, which is close to the low conductance group we observe [10]. As it is known that the oxidation of exTTF compounds results in the planarization and aromatization of the central three rings to the anthracene unit, the similarity in

Glycoluril–tetrathiafulvalene molecular clips: on the influence of electronic and spatial properties for binding neutral accepting guests

• Yoann Cotelle,
• Marie Hardouin-Lerouge,
• Stéphanie Legoupy,
• Olivier Alévêque,
• Eric Levillain and
• Piétrick Hudhomme

Beilstein J. Org. Chem. 2015, 11, 1023–1036, doi:10.3762/bjoc.11.115

• situ to the transient diene by reductive elimination using naked iodide [37][38][39] or the iodo-ionic liquid 1-butyl-3-methylimidazolium iodide [40]. After purification by column chromatography on silica gel, we noted that complete aromatization has occurred concomitantly and molecular clip 4 was

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

• subsequently the intermediate underwent intramolecular cyclization and oxidative aromatization to form the phenanthridine ring. Bowman et al. [16] modified this route for safety reasons by application of di(tert-butyl)peroxide as a source of the t-BuO• radical (Scheme 3). The required arylimines were prepared

• phenanthridines. Microwave-mediated intramolecular Diels–Alder cyclization of o-furyl(allylamino)arenes followed by spontaneous aromatization yielded dihydrophenanthridines, which upon exposure to UV light (315−400 nm) were oxidized into (aza)phenanthridines (Scheme 9) [26]. Synthetic pathways based on the

Aryl substitution of pentacenes

• Andreas R. Waterloo,
• Anna-Chiara Sale,
• Dan Lehnherr,
• Frank Hampel and
• Rik R. Tykwinski

Beilstein J. Org. Chem. 2014, 10, 1692–1705, doi:10.3762/bjoc.10.178

• was quenched with a proton source, and the resulting diol intermediates 5a–h were carried on directly to reductive aromatization with SnCl2/H2SO4 without further purification, ultimately yielding pentacene products 3a–h. While the isolation and characterization of diol products resulting from

• 4a was treated with a solution of biphenylmagnesium bromide in THF. After work-up and isolation of the intermediate diol 5i, reductive aromatization gave pentacene 3i in moderate yield over the two steps. Elaborating on the general idea of lateral functionalization, iodoaryl pentacene 3g offered an

C–H-Functionalization logic guides the synthesis of a carbacyclopamine analog

• Sebastian Rabe,
• Johann Moschner,
• Marina Bantzi,
• Philipp Heretsch and
• Athanassios Giannis

Beilstein J. Org. Chem. 2014, 10, 1564–1569, doi:10.3762/bjoc.10.161

• was thought to establish the C-nor-D-homo steroid system, and a gold-catalyzed amination/annulation/aromatization sequence was planned to install the pyridine F-ring. Diazo compound 3 originates from diene 4 through standard transformations, the latter being accessible from commercially available and

• /aromatization sequence (propargylamine, cat. Na[AuCl4]·2H2O, EtOH, 100 °C) [37][38] furnished, after removal of the tert-butyldimethylsilyl ether (tetrabutylammonium fluoride, THF, 25 °C), carbacyclopamine analog 2 in 36% overall yield for the two steps [39]. Carbacyclopamine analog 2 was then tested for its