Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• group, which has both an electronic (electron-withdrawing) and steric (e.g., CF3 vs a phenyl substituent [28]) component. Moreover, a comparison with the thermal conditions of the Diels–Alder reaction of 4-phenyl-1,1,1-trifluorobut-3-yn-2-one and cyclopentadiene [29] confirms the expected accelerating

• effect of the iminium activation. The Diels–Alder reaction of alkyne 1a with 2,3-dimethylbutadiene also occurred under very mild conditions and yielded the iminium-substituted 1,4-cyclohexadiene 4-Ch (Scheme 2), which, due to its high sensitivity toward moisture, was not purified but was further

• presumably renders an ionic [2 + 2] cycloaddition pathway competitive with the Diels–Alder reaction. The few reported examples of cyclobutene formation from alkynes and unactivated 1,3-dienes include the sensitized photocycloaddition of phenylacetylene and DMBD [30] and the gold(I)-catalyzed reaction of

One-pot and metal-free synthesis of 3-arylated-4-nitrophenols via polyfunctionalized cyclohexanones from β-nitrostyrenes

• Haruyasu Asahara,
• Minami Hiraishi and
• Nagatoshi Nishiwaki

Beilstein J. Org. Chem. 2020, 16, 1830–1836, doi:10.3762/bjoc.16.150

• School of Pharmaceutical Sciences, Osaka University, Yamadaoka 1-6, Suita, Osaka 565-0871, Japan 10.3762/bjoc.16.150 Abstract β-Nitrostyrenes underwent a Diels–Alder reaction with Danishefsky’s diene to afford cyclohexenes together with the corresponding hydrolyzed products, 3-arylated-5-methoxy-4

• with Danishefsky’s diene could be conducted in one pot to directly afford the corresponding nitrophenols. Moreover, a heteroaryl group, e.g., a thienyl group could be introduced into the nitrophenol framework. Keywords: 3-arylated-4-nitrophenol; Danishefsky’s diene; Diels–Alder reaction; nitroalkene

• reaction, a C2 unit possessing a nitro group and an aryl group at the vicinal position is incorporated into the products. This unique reactivity prompted us to probe the synthesis of the 3-arylated-4-nitrophenols 5 by the Diels–Alder reaction of nitrostyrenes 1 with Danishefsky’s diene (2, the

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• concomitant detrifluoromethylation. Furthermore, the Lewis acid-mediated retro Diels–Alder reaction was carried out uneventfully on product 61, affording the corresponding cyclopentenone 62 in moderate yield (Scheme 33). In order to rationalize the unexpected loss of the trifluoromethyl group upon

• conjugated addition of trimethylaluminum to form 66, followed by Lewis acid-mediated retro Diels–Alder reaction (Scheme 38). In another study by Riera and co-workers, they studied the influence of the olefin counterpart on the regioselectivity of the reaction [79]. Two olefins other than norbornadiene were

Models of necessity

• Timothy Clark and
• Martin G. Hicks

Beilstein J. Org. Chem. 2020, 16, 1649–1661, doi:10.3762/bjoc.16.137

• instance, an MO picture of the SN2 reaction is attractive but less common than the compact and informative “curly arrow” picture. The Diels–Alder reaction or aromaticity, on the other hand, cannot really be treated adequately within the Lewis picture without resorting to the Dewar–Zimmerman rules [80][81

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• 386, respectively, through another Diels–Alder reaction and an ene reaction [101] (Scheme 79). The reaction of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane (363) and quadricyclane (218) gave the bridged-thietane derivative 364 quantitatively in DMSO at 50 °C within 30 min [101] (Scheme 80). 3.3

Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole

• Carlos H. Escalante,
• Eder I. Martínez-Mora,
• Carlos Espinoza-Hicks,
• Alejandro A. Camacho-Dávila,
• Fernando R. Ramos-Morales,
• Francisco Delgado and
• Joaquín Tamariz

Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113

• propargyl bromide (14f) to generate pyrroles 8i,j, respectively, in high yields. The synthesis of octahydropyrrolo[3,4-e]indoles 9/10 was achieved through a Diels–Alder reaction between the 2-vinylpyrroles 8a–j and 16a,b and maleimides 7a–c under thermal conditions (Scheme 3). N-Unsubstituted 2

• ]. Theoretical calculations The Diels–Alder reaction of vinylpyrroles 8b, 8c and 8g with maleimides 7b and 7c resulted in a highly diastereoselective cycloaddition leading to the mixture of endo/exo cycloadducts 9/10, where the endo product 9 was the major one (Scheme 3 and Table 2). Considering the synthetic

• out to provide additional insights into the factors controlling the endo outcome [53][82][83][84][85], documenting in some cases a key role of NCIs in the preferential stereocontrol [86]. Conclusion The Diels–Alder reaction of N-substituted-2-vinylpyrroles 8a–j and N-unsubstituted-2-vinylpyrroles 16a

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

• Svetlana A. Kuznetsova,
• Alexander S. Gak,
• Yulia V. Nelyubina,
• Vladimir A. Larionov,
• Han Li,
• Michael North,
• Vladimir P. Zhereb,
• Alexander F. Smol'yakov,
• Artem O. Dmitrienko,
• Michael G. Medvedev,
• Igor S. Gerasimov,
• Ashot S. Saghyan and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99

• , including the ring opening of epoxides by water and alcohols. A Diels–Alder reaction between cyclopentadiene and methyl vinyl ketone was also catalyzed by F-1 in heptane. Depending on the polarity of the solvent mixture, the CAHOF F-1 could function as a purely heterogeneous catalyst or partly dissociate

• catalyst for the Brønsted acid-catalyzed ring opening reactions of epoxides with alcohols and water, with the latter reaction occurring in a three-phase medium. In addition, a Diels–Alder reaction was promoted by F-1 in heptane. Results and Discussion Mixing together aqueous solutions of two equivalents of

• partitioning of the epoxide into the aqueous phase was necessary for reaction to occur. Cyclohexene oxide (5) is, however, a good substrate under the same reaction conditions (Table 2, entry 5), possibly due to the greater reactivity of its fused bicyclic ring system. The Diels–Alder reaction of methyl vinyl

Diversity-oriented synthesis of 17-spirosteroids

• Benjamin Laroche,
• Thomas Bouvarel,
• Martin Louis-Sylvestre and
• Bastien Nay

Beilstein J. Org. Chem. 2020, 16, 880–887, doi:10.3762/bjoc.16.79

• Paris, Palaiseau Cedex, France 10.3762/bjoc.16.79 Abstract A diversity-oriented synthesis (DOS) approach has been used to functionalize 17-ethynyl-17-hydroxysteroids through a one-pot procedure involving a ring-closing enyne metathesis (RCEYM) and a Diels–Alder reaction on the resulting diene, under

• ) and lynestrenol (2). By using the sequence of RCEYM/Diels–Alder reaction, we rapidly synthesized "17-spirosteroid" compounds, orthogonally linking a non-steroidal polycyclic moiety to the steroid part at position 17. Spirocyclic systems play an important role in current medicinal chemistry thanks to

• Diels–Alder cycloadducts was demonstrated thanks to NOESY correlations observed between protons H-4', H-7'α at 2.30 ppm, H-8' at 3.46 ppm, and H-9' at 3.54 ppm, all on the same cyclohexene α-face. Overall, the facial selectivity of this Diels–Alder reaction seems controlled by the steric hindrance

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• et. al. [82]. The starting dienynes were obtained in a high enantiomeric purity starting form 2,6-dimethyl-1,4-benzoquinone and isoprene via an asymmetric Diels–Alder reaction. The domino metathesis reactions induced by the Grubbs second-generation catalyst proceeded in good yield (92%) thereby

• method, an enyne precursor was first converted into an exocyclic 1,3-diene in 92% yield. A Diels–Alder reaction with naphthoquinone and a deprotection step then led to the final compound (−)-zenkequinone B in a stereoselective manner (Scheme 23). C-Aryl glycosides Another interesting report from

• . Synthesis of spiro-C-aryl glycoside 24 by a tandem intramolecular enyne metathesis/Diels–Alder reaction/aromatization. Pathways to (−)-exiguolide (25) by Trost’s Ru-catalyzed enyne cross-coupling and cross-metathesis [94]. Funding Support from the Romanian Academy and from Wallonie-Bruxelles International

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• reactions and a newly developed deoxygenative aromatization procedure. The first enantioselective Diels–Alder reaction, which is an intermolecular cycloaddition and lactonization between (Z)-3-iodo-4-methylpenta-2,4-dien-1-ol (29) and methyl acrylate (30) in the presence of Mikami’s (binol)TiCl2 catalyst to

Mechanochemical Friedel–Crafts acylations

• Mateja Đud,
• Anamarija Briš,
• Iva Jušinski,
• Davor Gracin and
• Davor Margetić

Beilstein J. Org. Chem. 2019, 15, 1313–1320, doi:10.3762/bjoc.15.130

• mixture of 19 and 18 (3:2 ratio), accompanied with a small amount of 22. As a substitute for dianthracene 19, thermally more stable substrate, anthracene-N-methyl maleimide adduct 25 [54] was prepared by Diels–Alder reaction under high pressure conditions as well as by microwave-assisted reaction and

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• of a highly active carbocation Lewis acid catalyst. The stereocontrol potential of the chiral tritylium ion pair was demonstrated by its application in an enantioselective Diels–Alder reaction of anthracene. Keywords: anthracene; carbocation catalysis; Diels–Alder reaction; Fe(III)-based phosphate

• presence of strong Lewis acids [36]. We herein report the design and exploration of a new trityl carbocation that has a chiral weakly coordinating Fe(III)-based phosphate anion for the effective asymmetric catalysis in the Diels–Alder reaction of anthracenes. Results and Discussion In our previous work, we

• ; see Supporting Information File 1 for details). We next tested the metal phosphate strategy in the Diels–Alder reaction of anthracene, for which a catalytic asymmetric version has not been achieved yet. Recently, we reported that the tritylium salt [Ph3C][BArF], in situ generated by Ph3CBr and NaBArF

Synthesis of non-racemic 4-nitro-2-sulfonylbutan-1-ones via Ni(II)-catalyzed asymmetric Michael reaction of β-ketosulfones

• Alexander N. Reznikov,
• Anastasiya E. Sibiryakova,
• Marat R. Baimuratov,
• Eugene V. Golovin,
• Victor B. Rybakov and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2019, 15, 1289–1297, doi:10.3762/bjoc.15.127

• , which allows to obtain chiral cyclic sulfones with high enantioselectivity [10][11][12]. Also non-racemic cyclic sulfones can be obtained by the Diels–Alder reaction, catalyzed by chiral Lewis acids or organocatalysts. Rh- and Cu-catalyzed CH-insertion reactions occurring at moderate or high

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• presence of I2 as catalyst. The mechanism follows the initial formation of the imine compound between the aldehyde and the arylamine, followed by an imino-Diels–Alder reaction with the enolate generated from the ketosteroid. The reaction is highly regioselective for the enolization of the ketone, thus

Mechanochemical amorphization of chitin: impact of apparatus material on performance and contamination

• Thomas Di Nardo and
• Audrey Moores

Beilstein J. Org. Chem. 2019, 15, 1217–1225, doi:10.3762/bjoc.15.119

• atmosphere to relative degrees depending on equipment [5][26][27][28][29][30][31][32][33][34]. In particular, the Mack group has used an elegant strategy to evaluate the energy delivery for a Diels–Alder reaction performed under mechanochemical conditions and was able to correlate reactivity, or lack thereof

New terpenoids from the fermentation broth of the edible mushroom Cyclocybe aegerita

• Frank Surup,
• Florian Hennicke,
• Nadine Sella,
• Maria Stroot,
• Steffen Bernecker,
• Sebastian Pfütze,
• Marc Stadler and
• Martin Rühl

Beilstein J. Org. Chem. 2019, 15, 1000–1007, doi:10.3762/bjoc.15.98

• illudine [11], aromadendrane [12], marasmene [13] and fomannosane [14] type skeletons. Although bovistol could formally be supposed to be a triterpene, it is thought to be derived by a hetero-Diels–Alder reaction of two sesquiterpenes to form a dimeric sesquiterpenoid [15]. In the recently published genome

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• : asymmetric organocatalysis; axial chirality; biaryls; hydrogen bond; oxo-Diels–Alder reaction; Introduction The Diels–Alder (DA) reaction is a useful and easy-to-perform method for the synthesis of six-membered rings through the direct formation of C–C bonds between a diene and a dienophile (a substituted

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• applied a Diels–Alder reaction of 1,2,4,5-tetrazine with a terminal alkyne unit in a 21-crown-7-based [2]pseudorotaxane 14. The [2]rotaxane 15 was produced in 81% yield having pyridazine groups as stoppers (Figure 7). Very recently, Nierengarten and co-workers reported a solvent-free mechanochemical

Efficient synthesis of 4-substituted-ortho-phthalaldehyde analogues: toward the emergence of new building blocks

• Clémence Moitessier,
• Ahmad Rifai,
• Pierre-Edouard Danjou,
• Isabelle Mallard and
• Francine Cazier-Dennin

Beilstein J. Org. Chem. 2019, 15, 721–726, doi:10.3762/bjoc.15.67

• -methoxy-ortho-xylene in only 5% yield [14]. 4-HO-OPA was also described in 1997 by Taylor et al. as a crude product (via a Diels–Alder reaction of commercially available Danishefsky diene with 4,4-diethoxybut-2-ynal) for the synthesis of an antitumor analogue [15]. This aforementioned strategy was applied

Cyclopropene derivatives of aminosugars for metabolic glycoengineering

• Jessica Hassenrück and
• Valentin Wittmann

Beilstein J. Org. Chem. 2019, 15, 584–601, doi:10.3762/bjoc.15.54

• Diels–Alder reaction; metabolic engineering; Introduction Carbohydrates are an important class of biological molecules involved in many fundamental biological processes [1]. An important tool to visualize glycoconjugates in vitro and in vivo is metabolic glycoengineering (MGE) [2][3][4]. In this

Synthesis and biological investigation of (+)-3-hydroxymethylartemisinin

• Toni Smeilus,
• Farnoush Mousavizadeh,
• Johannes Krieger,
• Xingzhao Tu,
• Marcel Kaiser and
• Athanassios Giannis

Beilstein J. Org. Chem. 2019, 15, 567–570, doi:10.3762/bjoc.15.51

• not show any toxicity against L6 cells (a primary cell line derived from rat skeletal myoblasts). These results contribute to a better understanding of artemisinins mechanism of action. Keywords: artemisinin; biomimetic synthesis; Diels–Alder reaction; malaria; peroxides; Introduction The isolation

• the propargylic moiety with Red-Al. BAIB/TEMPO oxidation of this alcohol gave ketone 7. By a Reformatsky reaction of 7 using Zn/ethyl bromoacetate derivative 8 was obtained, which was subjected to a thermal (190 °C, toluene) intramolecular Diels–Alder reaction resulting in the formation of the β

A novel and efficient synthesis of phenanthrene derivatives via palladium/norbornadiene-catalyzed domino one-pot reaction

• Yue Zhong,
• Wen-Yu Wu,
• Shao-Peng Yu,
• Tian-Yuan Fan,
• Hai-Tao Yu,
• Nian-Guang Li,
• Zhi-Hao Shi,
• Yu-Ping Tang and
• Jin-Ao Duan

Beilstein J. Org. Chem. 2019, 15, 291–298, doi:10.3762/bjoc.15.26

• compound z-6 was isolated in 88% yield. Based on the above experimental results and the use of norbornadiene in Catellani reactions followed by retro-Diels–Alder reaction firstly reported by Lautens et al. [22][23][24], which is mentioned in recent works [11], a proposed mechanism for this domino reaction

• , G will experience immediate retro-Diels–Alder reaction after the catalytic cycle to afford the target product while taking off cyclopentadiene. Conclusion In summary, we have developed a novel and efficient protocol which allows us to construct a variety of phenanthrene derivatives starting from

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• tert-butyl ester function and finally hydrogenolytic opening of the isoxazolidine ring with simultaneous protection of the amino group (Scheme 18). By Diels–Alder reaction Acylnitroso derivative 74 prepared from methyl N-Boc-L-alaninate underwent Diels–Alder reaction with cyclopentadiene to produce

• [86][87][88] or a Diels–Alder reaction using acylnitroso compounds [89]. However, when compared with these multistep approaches hydroxylation of pyroglutamic acid derivatives seems to be the simplest option. Treatment of the lithium enolate of benzyl N-Boc-pyroglutamate (S)-86 with Davis oxaziridine

Mechanistic studies of an L-proline-catalyzed pyridazine formation involving a Diels–Alder reaction with inverse electron demand

• Anne Schnell,
• J. Alexander Willms,
• S. Nozinovic and
• Marianne Engeser

Beilstein J. Org. Chem. 2019, 15, 30–43, doi:10.3762/bjoc.15.3

• -substituted tetrazines via a Diels–Alder reaction with inverse electron demand has been studied with NMR and with electrospray ionization mass spectrometry. A catalytic cycle with three intermediates has been proposed. An enamine derived from L-proline and acetone acts as an electron-rich dienophile in a [4

• + 2] cycloaddition with the electron-poor tetrazine forming a tetraazabicyclo[2.2.2]octadiene derivative which then eliminates N2 in a retro-Diels–Alder reaction to yield a 4,5-dihydropyridazine species. The reaction was studied in three variants: unmodified, with a charge-tagged substrate, and with a

• formation of the enamine I seems plausible. It is an electron-rich dienophile which could undergo a [4 + 2] cycloaddition with the electron-poor aryl-substituted tetrazine 2 in a Diels–Alder reaction with inverse electron demand. The bicyclic Diels–Alder intermediate II then might undergo a retro-Diels

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• [50]. Further mutations within the cavity of NB provide a hydrophobic cavity. Several studies reported on the utilization of NB as scaffold for incorporated metal complexes, including the work of Hayashi et al. capitalizing on the polymerization of phenylacetylene [50][51], the Diels–Alder reaction