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

Tandem Cu-catalyzed ketenimine formation and intramolecular nucleophile capture: Synthesis of 1,2-dihydro-2-iminoquinolines from 1-(o-acetamidophenyl)propargyl alcohols

• Gadi Ranjith Kumar,
• Yalla Kiran Kumar,
• Ruchir Kant and
• Maddi Sridhar Reddy

Beilstein J. Org. Chem. 2014, 10, 1255–1260, doi:10.3762/bjoc.10.125

• alcohols with various sulfonyl azides is found to undergo a concomitant intramolecular nucleophile attack to generate 1,2-dihydro-2-iminoquinolines after aromatization (via elimination of acetyl and hydroxy groups) and tautomerization. The reaction produces 4-substituted and 3,4-unsubstituted title

• the tentative intermediate 6. As expected, the reaction on 2a proceeded through a 6-membered cyclization to form 7 which underwent aromatization via elimination of acetic acid to produce 8. Product 8 exists in tautomerized form of 9 (vide infra, X-ray structure of 9j). In fact, an elegant synthesis of

Visible-light photoredox catalyzed synthesis of pyrroloisoquinolines via organocatalytic oxidation/[3 + 2] cycloaddition/oxidative aromatization reaction cascade with Rose Bengal

• Carlos Vila,
• Jonathan Lau and
• Magnus Rueping

Beilstein J. Org. Chem. 2014, 10, 1233–1238, doi:10.3762/bjoc.10.122

• /oxidative aromatization cascade using Rose Bengal as an organo-photocatalyst. A variety of pyrroloisoquinolines have been obtained in good yields under mild and metal-free reaction conditions. Keywords: alkaloids; [3 + 2] cycloaddition; organocatalysis; oxidation; photochemistry; photoredox catalysis; Rose

• ]isoquinolines. Wang and co-workers described a copper catalyzed oxidation/[3 + 2] cycloaddition/aromatization cascade [28]. Also, Xiao disclosed a very elegant oxidation/[3 + 2] cycloaddition/aromatization cascade catalyzed by [Ru(bpy)3]3+ under irradiation with visible light [29]. In this context, very

• ] cycloaddition/aromatization cascade catalyzed by Rose Bengal under irradiation with green LEDs. Results and Discussion Initially, we focused on the reaction between methyl dihydroisoquinoline ester 1a and N-methylmaleimide (2a) catalyzed by Rose Bengal. Although the [3 + 2] cycloaddition occurs smoothly in the

First synthesis of meso-substituted pyrrolo[1,2-a]quinoxalinoporphyrins

• Dileep Kumar Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2014, 10, 808–813, doi:10.3762/bjoc.10.76

• 5 minutes, followed by aromatization in the presence of KMnO4 at room temperature (Scheme 1). The target products were purified by column chromatography over neutral alumina and obtained in 60–76% isolated yields. Furthermore, the π electron-rich free-base porphyrin dyads (4g and 4h) were converted

Copper–phenanthroline catalysts for regioselective synthesis of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines/phenanthrolines and of pyrrolo[1,2-a]phenanthrolines under mild conditions

• Rupankar Paira,
• Tarique Anwar,
• Maitreyee Banerjee,
• Yogesh P. Bharitkar,
• Shyamal Mondal,
• Sandip Kundu,
• Abhijit Hazra,
• Prakas R. Maulik and
• Nirup B. Mondal

Beilstein J. Org. Chem. 2014, 10, 692–700, doi:10.3762/bjoc.10.62

• 14a–c in high yield. It is interesting to note that every reaction proceeded only up to the cycloaddition stage, without any aromatization of the final cycloadduct. However, a similar reaction of phenanthroliniums 12a,b with alkyne dipolarophiles like acetylenedicarboxylates or monocarboxylates 13a–d

• proceeded with aromatization of the putative dihydroaromatic intermediates to produce the final cycloaddition products 14d–g. Characterization of the products was done via mass and NMR spectral studies. Furthermore, the single-crystal X-ray study of cycloadduct 14e undoubtedly confirmed the structure of

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• attack of the oxygen nucleophile to the Au-activated triple bond. Aromatization and protodeauration closed the catalytic cycle to give furans 12 and to regenerate the catalyst (Scheme 11). A conceptually similar approach – and a comparable mechanism – was proposed by Ohno and Fujii for the synthesis of

• , which by loss of the tosyl group and base-catalyzed aromatization yields the H-pyrazolo[5,1-a]isoquinoline 48. Finally, a new series of fully aromatic pyrazolo[5,1-a]isoquinolines 53, bearing an amino group in position 2 can be synthesized under silver triflate catalysis by the usual three-component

An oxidative amidation and heterocyclization approach for the synthesis of β-carbolines and dihydroeudistomin Y

• Suresh Babu Meruva,
• Akula Raghunadh,
• Raghavendra Rao Kamaraju,
• U. K. Syam Kumar and
• P. K. Dubey

Beilstein J. Org. Chem. 2014, 10, 471–480, doi:10.3762/bjoc.10.45

• (1) are generally carried out either from indole or its suitably substituted derivatives. The acylation of 2-(3-indolyl)ethyl isocyanide with phenylacetyl chloride followed by cyclization and aromatization is well documented in the literature for the synthesis of 1-benzoyldihydro-β-carbolines. The

• reported the synthesis of fascaplysin (4) by the reaction of tryptamine with phenylacetyl chloride and carried out the aromatization under photo-oxidation conditions [15][16]. Lindsley and co-workers [17] reported the synthesis of eudistomins Y1−Y7 (6a–6g) under microwave conditions [18]. Considering the

• . Accordingly eudistomin Y (6) could be obtained by the aromatization of dihydro-β-carboline 12. The dihydro-β-carboline 12 in turn could be synthesized from ketoamide 9 under Lewis acid mediated Bischler–Napieralski reaction. The key intermediate, ketoamide 9 required for the synthesis could easily be accessed

Organobase-catalyzed three-component reactions for the synthesis of 4H-2-aminopyrans, condensed pyrans and polysubstituted benzenes

• Moustafa Sherief Moustafa,
• Saleh Mohammed Al-Mousawi,
• Maghraby Ali Selim,
• Ahmed Mohamed Mosallam and
• Mohamed Hilmy Elnagdi

Beilstein J. Org. Chem. 2014, 10, 141–149, doi:10.3762/bjoc.10.11

• generate 10 that cyclizes to form 12. Subsequent aromatization of 12 produces the benzoate derivative 13b. Alternatively, 8 could react with malononitrile to yield 11 that then serve as a precursor to 13 (Scheme 4). In support of the former mechanistic proposal, it was observed that 2-amino-4H-pyran 9

One-pot cross-enyne metathesis (CEYM)–Diels–Alder reaction of gem-difluoropropargylic alkynes

• Santos Fustero,
• Paula Bello,
• Javier Miró,
• María Sánchez-Roselló,
• Günter Haufe and
• Carlos del Pozo

Beilstein J. Org. Chem. 2013, 9, 2688–2695, doi:10.3762/bjoc.9.305

• diethyl acetylenedicarboxylate (DEAD) afforded adduct 3c in 51% yield, and no aromatization was observed during the process (Table 1, method A, entry 3). When maleic anhydride was used as dienophile, the corresponding diacid 3f, arising from the anhydride ring opening under the reaction conditions, was

• –10). Finally, fluorinated ketones could also be used as substrates for the sequential process (Table 1, method A, entries 12–15) and again with alkynes as dienophiles, no aromatization of the final products was detected (Table 1, method A, entry 12). The yields that appear in Table 1 in the last

New syntheses of 5,6- and 7,8-diaminoquinolines

• Maroš Bella and
• Viktor Milata

Beilstein J. Org. Chem. 2013, 9, 2669–2674, doi:10.3762/bjoc.9.302

• -benzoselenadiazole skeleton while the pyridine ring can be obtained by transformation of the pyridone core [15]. The synthesis of 7,8-diaminoquinoline (3) starting from selenadiazolo[3,4-h]quinolone 1 is depicted in Scheme 1. In the first step, the aromatization of the pyridone ring by chlorination with POCl3 in DMF

Gold(I)-catalyzed domino cyclization for the synthesis of polyaromatic heterocycles

• Mathieu Morin,
• Patrick Levesque and
• Louis Barriault

Beilstein J. Org. Chem. 2013, 9, 2625–2628, doi:10.3762/bjoc.9.297

• to the carboxonium provides the sulfonium 10 which upon protodeauration and aromatization gives 7 [20][21][22][23][24][25]. Other polar solvents such as acetone and dichloromethane were employed without much success. One might consider that the high polarity of nitromethane helps to alleviate the

Flexible synthesis of anthracycline aglycone mimics via domino carbopalladation reactions

• Markus Leibeling and
• Daniel B. Werz

Beilstein J. Org. Chem. 2013, 9, 2194–2201, doi:10.3762/bjoc.9.258

• . Subsequent aromatization of the C-ring and several additional steps generated the daunomycin aglycon 6 and the corresponding isodaunomycin aglycone (dependent on the regioisomers) in a total of 16 steps. In 2003, Saá published a concise route to anthraquinone derivatives by using an intramolecular dehydro

The chemistry of isoindole natural products

• Klaus Speck and
• Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

• described for the biogenesis of (S)-reticuline (101) (compare Scheme 11). A de-aromatizing spirocyclization of 121 leads to (R)-orientalinone (122), which, after reduction of the ketone to the secondary alcohol 123, undergoes a [1,2]-alkyl migration with concomitant loss of water. Re-aromatization and

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

• Ir4+(ppy)3 that is reduced to the initial catalyst, Ir(ppy)3. Deprotonation of amine radical cation 124 by NaOAc produces α-amino radical 125, which is coupled with radical anion 123 to form the key C–C bond in 126. Finally, aromatization via expulsion of the nitrile group provides benzylic amine 127

Cyclization of substitued 2-(2-fluorophenylazo)azines to azino[1,2-c]benzo[d][1,2,4]triazinium derivatives

• Aleksandra Jankowiak,
• Emilia Obijalska and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2013, 9, 1873–1880, doi:10.3762/bjoc.9.219

• photostationary state establishes providing a constant ratio of Z- to E-isomers. Previous analyses suggested [7] that the cyclization of 4-Z involves 6 π electrons leading to non-aromatic product 10, which upon Ca2+-assisted departure of the fluoride undergoes aromatization and formation of cation 1. In this work

• have been formed, but were presumably unstable under the reaction conditions, as already observed for 1d. Also consistent with the computational results is the observation that the formation of 1 requires a fluoride scavenger, apparently for the aromatization of the cyclic product. The analysis of

• formation of the triazinium cations is accomplished by aromatization of the cyclic product by Ca2+ ion-assisted removal of the fluoride. These results are supported by experimental data, which demonstrate a facile conversion of all azoazines under the reaction conditions, although only 5 out of 8 triazinium

An organocatalytic route to 2-heteroarylmethylene decorated N-arylpyrroles

• Alexandre Jean,
• Jérôme Blanchet,
• Jacques Rouden,
• Jacques Maddaluno and
• Michaël De Paolis

Beilstein J. Org. Chem. 2013, 9, 1480–1486, doi:10.3762/bjoc.9.168

• electronically deficient pyridyl residue was also converted into 5e (80%) while pyrrolidine 4f bearing a pyrazine core underwent aromatization with high efficiency to give 5f (97%). The C2-symmetric scaffold 4g was efficiently converted into 5g (86%) and similar treatment of pyrimidine 4h provided pyrrole 5h in

• the exo-enamine into the endo compound under basic treatment [26]. These observations suggest that DBU or KCN behave as base to promote the deconjugation of the acrylate moiety of 4a [27]. The resulting product 4a’ would lead under basic treatment to pyrroline 4a” from which aromatization to 5a would

A versatile and efficient approach for the synthesis of chiral 1,3-nitroamines and 1,3-diamines via conjugate addition to new (S,E)-γ-aminated nitroalkenes derived from L-α-amino acids

• Vera Lúcia Patrocinio Pereira,
• André Luiz da Silva Moura,
• Daniel Pais Pires Vieira,
• Leandro Lara de Carvalho,
• Eliz Regina Bueno Torres and
• Jeronimo da Silva Costa

Beilstein J. Org. Chem. 2013, 9, 832–837, doi:10.3762/bjoc.9.95

• , followed by HNO2 elimination leading to aromatization. There are a few reports in the literature where the azide anion is added to α,β-unsaturated nitroalkenes [8][19][20][21][22] forming 1,4-adducts [8] or 1,2,3-triazole derivatives [31][32][33]. Apparently, the reaction course depends on the temperature

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

• Maurizio Fagnoni,
• Stefano Protti,
• Davide Ravelli and
• Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

• -aromatization gave an alkylated aromatic (A–D, path c → d), while trapping of the radical by an electron-withdrawing substituted alkene T (step e) [28][29] followed by BET from the radical anion (step f) of the acceptor (that was thus recovered) led to photocatalyzed alkylation of the alkene [5][30][31]. Both

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• there are two α-hydrogen atoms in the adduct aromatization can be accomplished by base treatment (e.g. formation of 153 and 156). Incorporation of substituents into the double bond of the dienophile slows down the addition process or prevents it completely. Unusual dienophiles such as cyclobutadiene or