Inductive heating and flow chemistry – a perfect synergy of emerging enabling technologies

• Conrad Kuhwald,
• Sibel Türkhan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2022, 18, 688–706, doi:10.3762/bjoc.18.70

• the residence times of the reactions outperformed those of the analogous experiments carried out under batch conditions by far [62][63][64]. The heating method was also successfully tested on various thermally conducted pericyclic reactions (Scheme 10, case A), such as in (hetero)-Diels–Alder

• reactions (anthracene (33) and maleic anhydride (34) to the cycloaddition adduct 35 and chromene carbaldehyde 36 and enol ether 37 to the diastereomeric pyrano-chromenes 38), Alder-En reactions (oxomalonate diethyl ester (39) and β-pinene (40) to give the α-pinene derivative 41), and the thermal

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• demethoxycarbonylating annulation of methyl methacrylate (33) with 3-cyanophthalide (32), in the presence of lithium tert-butoxide as catalyst (64% yield) (Scheme 7) [91]. Recently, Dissanayake and co-workers tested the stability of furans to be used as a diene in Diels–Alder reactions for the synthesis of p

• reaction, among pericyclic reactions, is a very important synthetic approach to obtain several molecular scaffolds, including naturally occurring molecules, drugs, polymers, and heterocycles with promising biological activity. Especially, Diels–Alder reactions involving quinones and dienes as starting

• of asymmetric compound 50 catalyzed by a chiral oxazaborolidinium cation (49) [107]. This type of catalyst has been used in several Diels–Alder reactions proving to be an excellent choice for highly enantioselective reactions [108]. For instance, the reaction of menadione (10) with 2

Borylated norbornadiene derivatives: Synthesis and application in Pd-catalyzed Suzuki–Miyaura coupling reactions

• Robin Schulte and
• Heiko Ihmels

Beilstein J. Org. Chem. 2022, 18, 368–373, doi:10.3762/bjoc.18.41

• based on Diels–Alder reactions of cyclopentadiene with alkynes [13][14][15][16][17][18][19][20][21][22][23]. However, since this synthetic route requires strongly electrophilic alkynes, its scope is limited to products that contain at least one electron-acceptor group, such as an ester, a nitrile or

Site-selective reactions mediated by molecular containers

• Rui Wang and
• Yang Yu

Beilstein J. Org. Chem. 2022, 18, 309–324, doi:10.3762/bjoc.18.35

• . Review Cycloaddition/addition Cycloaddition reactions have long been applied to molecular container-mediated enzyme-mimicking transformations [27][31][32][33], and the Fujita group has done pioneering research works in this direction [27][34]. In 2006, the authors reported unique Diels–Alder reactions of

• reports of supramolecular host-mediated Diels–Alder reactions of anthracenes, 9,10-adducts bridging the center rings of the anthracene frameworks were generally yielded [35][36][37], which resulted from the high localization of π-electron density at that sites [38]. Besides, these reactions required near

• reactions. Naphthalene is usually hard to undergo Diels–Alder reactions [44][45][46], even though the quantum-mechanical and thermochemical calculations suggest that the reaction is exothermic, which indicates the entropic cost is significant [47]. In 2010, the same group reported another interesting site

Synthesis of novel [1,2,4]triazolo[1,5-b][1,2,4,5]tetrazines and investigation of their fungistatic activity

• Anna V. Korotina,
• Svetlana G. Tolshchina,
• Rashida I. Ishmetova,
• Natalya P. Evstigneeva,
• Natalya A. Gerasimova,
• Natalya V. Zilberberg,
• Nikolay V. Kungurov,
• Gennady L. Rusinov,
• Oleg N. Chupakhin and
• Valery N. Charushin

Beilstein J. Org. Chem. 2022, 18, 243–250, doi:10.3762/bjoc.18.29

• labeling proteins and visualizing cancer due to the ability of s-tetrazine to fast and biocompatible ligation with alkenes via the inverse electron demand Diels–Alder reactions [29][30][31]. At the same time, azolo-annulated 1,2,4,5-tetrazines remain to be a scarcely studied class of compounds, mainly due

High-speed C–H chlorination of ethylene carbonate using a new photoflow setup

• Takayoshi Kasakado,
• Takahide Fukuyama,
• Tomohiro Nakagawa,
• Shinji Taguchi and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2022, 18, 152–158, doi:10.3762/bjoc.18.16

• [14][15][16][17][18][19][20]. Vinylene carbonate also serves as a useful synthetic building block for Diels–Alder reactions [21][22][23][24][25] and polymerization [26][27][28][29][30]. Results and Discussion Using a PTFE tube and PTFE connectors, we connected the photoflow setup with a chlorine gas

Efficient synthesis of polyfunctionalized carbazoles and pyrrolo[3,4-c]carbazoles via domino Diels–Alder reaction

• Ren-Jie Fang,
• Chen Yan,
• Jing Sun,
• Ying Han and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2021, 17, 2425–2432, doi:10.3762/bjoc.17.159

• successfully developed several efficient synthetic protocols for diversely functionalized tetrahydrocarbazoles and the corresponding carbazole derivatives [41][42][43][44][45][46][47]. To further demonstrate the synthetic application of domino Diels–Alder reactions and in continuation of our aim to providing

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• 157 under reflux with concentrated HCl [69]. Synthesis of anthraquinone derivatives Friedel–Crafts intramolecular cyclization In 2013, Hilt and co-workers synthesized symmetric and asymmetric anthraquinone derivatives 162 bearing Br, Me, or OMe groups via ZnI2-catalyzed Diels–Alder reactions/DDQ

• metathesis strategy to synthesize benz[a]anthracenes. Green synthesis of oxa-aza-benzo[a]anthracene and oxa-aza-phenanthrene derivatives. Triple benzannulation of substituted naphtalene via a 1,3,6-naphthotriyne synthetic equivalent. Zinc iodide-catalyzed Diels–Alder reactions with 1,3-dienes and aroyl

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• , and diverse transformations are known to create new C–C bonds and/or to extend the (poly)cyclic system. In this context, cycloadditions are of special importance, and Diels–Alder reactions have successfully been explored in conversions aimed at the construction of a new, six-membered ring [5]. However

Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles

• Ramazan Koçak and
• Arif Daştan

Beilstein J. Org. Chem. 2021, 17, 719–729, doi:10.3762/bjoc.17.61

• reaction conditions. Inverse electron-demand Diels–Alder reactions are cycloadditions between electron-rich dienophiles and electron-poor dienes. EDGs raise the electron density of dienes and, in parallel, raise the LUMOdiene–HOMOdienophile energy gap, and consequently the reactivity decreases. Although

• . Structures of s-tetrazines 2a–l. UV–vis spectra of 3c–f and 3k in CH3CN at rt (c = 5 μM). Fluorescence spectra of 3c–f and 3k in CH3CN at rt (c = 5 μM). Ambient (top) and fluorescence (bottom, under 365 nm UV light) images of 3c–f and 3k in CH3CN. Inverse electron-demand Diels–Alder reactions of

• dibenzosuberenone (1) with tetrazines 2a–l. Inverse electron-demand Diels–Alder reactions between dibenzosuberenone 1 and tetrazines 2ka and 2lb. a5.55 mmol 1, 3.70 mmol 2k, 10 mL toluene, 120 ˚C, 48 h. b4.85 mmol 1, 0.98 mmol 2l, 100 ˚C, overnight (solvent free). Proposed reaction mechanism for the formation of

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors

• Emine Kayahan,
• Mathias Jacobs,
• Leen Braeken,
• Leen C.J. Thomassen,
• Simon Kuhn,
• Tom van Gerven and
• M. Enis Leblebici

Beilstein J. Org. Chem. 2020, 16, 2484–2504, doi:10.3762/bjoc.16.202

• an ene reaction of β-citronellol and Diels–Alder reactions of α-terpinene and (5-methylfuran-2-yl)methanol [46] as well as the synthesis of cyclopent-2-enones from furans [47] and the synthesis of diverse γ-lactam scaffolds [48]. Conversions larger than 90% were achieved for all reactions [46][47][48

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• providing the stereoinformation necessary for induction during the C–C bond formation. Catalytic approaches for C–C bond-forming reactions even found their way into the relatively young field of supramolecular chemistry, e.g., regioselective Diels–Alder reactions within supramolecular hosts as described by

• Fujita et al. [9][10][11] or stereoselective nucleophilic substitutions by Raymond et al. [12] are important examples in this context. Recently, we described the use of hierarchically assembled helicates as templates for stereoselective Diels–Alder reactions via a post-functionalization process [13

• as homogeneous catalysts. Results and Discussion Stereoselective Diels–Alder reactions in the periphery of hierarchically assembled helicates Elucidating the induction pathway of the Diels–Alder reaction is vital for the optimization of the system described above and for the development of future

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

• iminium salts. Herein we present several reactions which are based on the electron-poor acetylenic bond and on the high electrophilicity of the CF3-substituted iminium group. These salts were found to be highly reactive dienophiles in Diels–Alder reactions with cyclopentadiene, 2,3-dimethylbutadiene and

• and therefore, are candidates for polar Diels–Alder reactions [40][41]. The thermal cyclization of Diels–Alder adducts as shown in Scheme 2 and Scheme 3 appear to be the first intramolecular SE(Ar) reactions of an α-(trifluoromethyl)iminium functional group. Analogous intermolecular reactions of CF3

• ] cycloaddition reactions [45]. Thus, while styrene and maleic anhydride react only at elevated temperatures, with the more electrophilic (methoxycarbonyl)maleic anhydride two 2:1 adducts are already formed at room temperature: one by two consecutive Diels–Alder reactions, the other one by a Diels–Alder/ene

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

• Diels-Alder reactions [70]. Tentative mechanism for the nucleophilic addition/retro-aldol reaction sequence. Catalytic PKR with norbornadiene [70]. Scope of the PKR of trifluoromethylalkynes with norbornadiene [72]. DBU-mediated detrifluoromethylation [72]. A simple route to enone 67, a common

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

• aromatization of the polycyclic intermediates provides the corresponding polycyclic pyrrolo-isoindoles and isoindolo-pyrrolo-indoles. A theoretical study on the stereoselective Diels–Alder reactions, carried out by calculating the endo/exo transition states, revealed the assistance of non-covalent interactions

• provide compounds 12. To account for the strong endo preference of adducts 9, a computational study was performed to analyze the stationary points on the potential surfaces of the Diels–Alder reactions. Results and Discussion Synthesis Pyrroles 8a–j were prepared through a straightforward and efficient

• tetrahydroindole skeleton) [32]. Any attempt to isolate or detect 17 during the trials turned out to be unsuccessful [35]. It is noteworthy that there have been almost no reports to date on the uncommon highly diastereoselective Diels–Alder reactions of analogous 2-vinyl or 3-vinylpyrroles [32], nor on the

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

• the propargylic alcohol, the resulting enyne is a good substrate for ring closing enyne metathesis (RCEYM) towards new diene substrates [40][41][42], which can be employed in Diels–Alder reactions with a variety of dienophiles (Figure 1) [43][44][45][46][47][48][49][50][51][52][53][54]. This strategy

• study (Scheme 2). Thus, in the presence of G-II in toluene and under microwave heating, the reaction provided 17-spirosteroid dienes 8–10 in good yields (67–82%). Spirocyclic vinylcyclopentene substrates 8a,b and 9a,b were engaged in Diels–Alder reactions with a variety of dienophiles (11–15). The

• 84% yield. Concerning the use of oxepane-type dienes 8b and 9b, none of the attempted Diels–Alder reactions proved efficient, systematically leading to a mixture of diastereoisomers and difficult purifications. Only cycloadducts 16f and 17b could be isolated in minute amounts (Scheme 3). Finally, the

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

• assembly of the subunits leading to the pentacyclic scaffold. Previously, the AB ring system of manzamines was constructed mainly using Diels–Alder reactions [84][85]. Thus, Fukuyama et al. [85] described an elegant approach for the synthesis of (+)-manzamine A in a totally stereoselective manner relying

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• temperature (Scheme 4) [94]. In their study, they observed that electron-donating groups provided better yields as compared to electron-withdrawing groups. The earlier reported methods for the synthesis of fluorenones, viz, Friedel–Craft acylations [95][96], oxidations of fluorenes [97][98], and Diels–Alder

• reactions [99], generated a lot of waste products. Therefore, this methodology seemed to be far better as compared to previously reported methods. With the help of this strategy, the group assembled several fluorenones that could further be functionalized to generate other interesting molecules. As can be

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• undergo Diels–Alder reactions with electron-rich dienophiles [13][14][15][16][17], treatment of 5 with Fukuzumi’s catalyst [18] under illumination with blue light only led to decomposition of the starting material (Table 1, entry 15). Notably, a photoredox catalyst with a lower oxidation potential could

Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts

• Kenta Tanaka,
• Yuta Tanaka,
• Mami Kishimoto,
• Yujiro Hoshino and
• Kiyoshi Honda

Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208

• green light irradiation [24][25]. In the course of this study, we found that these thioxanthylium photocatalysts efficiently oxidized styrene derivatives such as trans-anethole, and promoted radical cation Diels–Alder reactions. Based on the background mentioned above, in order to expand the utility of

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• reaction and as organocatalysts in Diels–Alder reactions [27]. The group of Metrangolo also reported halogen bonding-promoted catalysis in water by exploiting a halogen bonding amino acid, which combines excellent donor properties with good water solubility [28], in addition to their seminal contributions

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

• reviewed in this article. Syntheses were clustered based on: i) syntheses using tetralone (Figure 2, route A nad B), ʟ-abietic acid and/or ʟ-dehydroabietic acid as starting materials (route C, D and E); ii) syntheses using Diels–Alder reactions for the construction the A, B and C-rings (route F and G); iii

• -elimination and acid hydrolysis to give the key triptophenolide methyl ether (8) in racemic form (16.5%). In 2008, Sherburn and co-workers developed an approach to the formal synthesis of triptolide (Figure 2, route G, Scheme 5) [71]. Key features of the synthesis include two intermolecular Diels–Alder

• 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

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• separation. This problem was resolved by the introduction of scandium triflate (Sc(OTf)3) as a promising reusable Lewis acid in Diels–Alder reactions by Kobayashi [78]. However, in recent years scandium(III) trifluoromethanesulfonate (Sc(OTf)3) has emerged as an efficient, mild, commercially available

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

• -coordinated phosphonate anion with balanced association ability with tritylium ions provided a new opportunity in pursuing chiral ion pair-type carbocation catalysis. The resulted asymmetric tritylium catalysis has enabled the so-far challenging Diels–Alder reactions of unsubstituted anthracene with good

Ugi reaction-derived prolyl peptide catalysts grafted on the renewable polymer polyfurfuryl alcohol for applications in heterogeneous enamine catalysis

• Alexander F. de la Torre,
• Gabriel S. Scatena,
• Oscar Valdés,
• Daniel G. Rivera and
• Márcio W. Paixão

Beilstein J. Org. Chem. 2019, 15, 1210–1216, doi:10.3762/bjoc.15.118

• -supported catalysts amenable for continuous-flow asymmetric enamine catalysis [9][10]. The acid-catalyzed polymerization of furfuryl alcohol renders a dark polymer featuring a complex cross-linked polyunsaturated scaffold derived from polycondensation and Diels–Alder reactions [11][12]. Worldwide, there is