Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• Melchiorre. A Diels–Alder reaction of indole-2,3-quinodimethane 76 (generated from 77 and the prolinol catalyst 78 ) with the enone 79 affords a tetrahydrocarbazole derivative 80. The NHC precatalyst 22 then promotes an intramolecular cross-benzoin condensation of the keto-aldehyde to furnish the tetracyclic

• cycloadducts 84 in good yield and enantioselectivity [63]. Initially, the trienamine 85 is generated by the action of prolinol catalyst 86 on the dienal 82. The former (85) then undergoes a Diels–Alder reaction with the sulfonylimine 83 to generate the keto-aldehyde 87. Finally, the NHC precatalyst 22 mediates

Self and directed assembly: people and molecules

• Tony D. James

Beilstein J. Org. Chem. 2016, 12, 391–405, doi:10.3762/bjoc.12.42

• catalyst of diastereoselective aza-Diels–Alder reactions [68] (Figure 14). While, the structure of the “chiral boron reagent” still remains unknown during our investigation of analogues we discovered a very interesting three-component self-assembly. Chiral binol, a chiral amine and 2-formylbenzeneboronic

• in 2002. (Left) Private photo taken in Osaka. (Right) Photo taken in Tokyo by Katsuhiko Ariga. Preparation of chiral boron reagent and use as catalyst for aza-Diels–Alder reactions. Chiral three component self-assembling system. Reaction of trimethylsilyl cyanide with tricarbonyl (η5-cyclohexadienyl

A quadruple cascade protocol for the one-pot synthesis of fully-substituted hexahydroisoindolinones from simple substrates

• Hong-Bo Zhang,
• Yong-Chun Luo,
• Xiu-Qin Hu,
• Yong-Min Liang and
• Peng-Fei Xu

Beilstein J. Org. Chem. 2016, 12, 253–259, doi:10.3762/bjoc.12.27

• isoindolinones have been developed. The first method was the synthesis of 3-substituted isoindolinones from the corresponding N-methylmaleimides by the Diels–Alder reaction with 1,3-butadiene followed by hydrogenation. The second and the third methods employed the corresponding dicarboxylic acids and the

My maize and blue brick road to physical organic chemistry in materials

• Anne J. McNeil

Beilstein J. Org. Chem. 2016, 12, 229–238, doi:10.3762/bjoc.12.24

• by our surprising substituent effects on the Diels–Alder regioselectivity in our monomer synthesis. Together we designed a collaborative project to further evaluate these effects. These studies led us to conclude that the π system is relatively unimportant and that substituent effects can instead be

Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands

• Julia Wappel,
• Roland C. Fischer,
• Luigi Cavallo,
• Christian Slugovc and
• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 154–165, doi:10.3762/bjoc.12.17

• polymerization of DCPD is their outstanding solubility in the neat monomer. The main challenge of the polymerization of DCPD is to guarantee an adequate mixing of monomer and catalyst to obtain a homogenous reaction mixture and moreover a steady polymerization product. DCPD is also prone to undergo a retro-Diels

• –Alder reaction at higher temperatures, causing a mass loss during polymerization if higher temperatures are applied for the reaction. To test the pre-catalysts regarding their performance in the polymerization of DCPD, two different test-reactions were carried out: a) STA measurements to gain an insight

A journey in bioinspired supramolecular chemistry: from molecular tweezers to small molecules that target myotonic dystrophy

• Steven C. Zimmerman

Beilstein J. Org. Chem. 2016, 12, 125–138, doi:10.3762/bjoc.12.14

• related class of achiral molecular tweezers was developed by Klärner et al., with their first report appearing in 1996 [32]. These di-, tri-, and tetramethylene-bridged aromatic systems (e.g., 19 and 20) were prepared by consecutive Diels–Alder reactions and have been shown to exhibit a remarkably rich

Synthesis and reactivity of aliphatic sulfur pentafluorides from substituted (pentafluorosulfanyl)benzenes

• Norbert Vida,
• Jiří Václavík and
• Petr Beier

Beilstein J. Org. Chem. 2016, 12, 110–116, doi:10.3762/bjoc.12.12

• -benzoquinone with cyclopentadiene afforded the Diels–Alder adducts. Decomposition of 3-(pentafluorosulfanyl)muconolactone in acidic, neutral and basic aqueous media was investigated and the decarboxylation of 2-(pentafluorosulfanyl)maleic acid provided 3-(pentafluorosulfanyl)acrylic acid. Keywords

• : dearomatization; decarboxylation; Diels–Alder reaction; oxidation; pentafluorosulfanyl group; Introduction Fluorinated organic compounds have been one of the foci of chemical industry for the last several decades. The unique properties of fluorine atoms and fluorinated groups have been exploited in various

• oxidation of aromatics. Benzoquinone 12 is a solid material with good stability at −20 °C. Several standard reactions were investigated. Reduction to hydroquinone 15 using catalytic palladium was very efficient (Scheme 5). The Diels–Alder reaction with cyclopentadiene proceeded in a high yield at ambient

Solving the puzzling competition of the thermal C²–C⁶ vs Myers–Saito cyclization of enyne-carbodiimides

• Anup Rana,
• Mehmet Emin Cinar,
• Debabrata Samanta and
• Michael Schmittel

Beilstein J. Org. Chem. 2016, 12, 43–49, doi:10.3762/bjoc.12.6

• computations, we were unable to locate any diradical intermediate along the C2–C6 (Schmittel) channel. Rather the results indicate that all enyne-carbodiimides 7a–c follow a concerted intramolecular Diels–Alder (DA) pathway toward the DA products 9DA (Figure 1), which subsequently rearrange to the isolated

• enyne-carbodiimides 7a and 7c are significantly lower at 32.2 and 32.8 kcal mol−1, respectively. Disturbingly, though, the computations predict in all cases a strong kinetic preference for the Myers–Saito (Figure 1) over the concerted C2–C6 (DA) pathway. The C2–C6 Diels–Alder TS 7a_TSDA is 3.8 kcal mol

• represent the respective free energies in kcal mol–1 at 138 °C. Subscripts “DA”, “MS” and “HT” stand for “Diels–Alder”, “Myers–Saito” and “Hydrogen Transfer”, respectively. Thermal cyclization modes of enyne-carbodiimides 1a–c. Thermolysis of enyne-carbodiimides 7a–c furnishing 8a–c [19]. Synthesis of enyne

Iron complexes of tetramine ligands catalyse allylic hydroxyamination via a nitroso–ene mechanism

• David Porter,
• Belinda M.-L. Poon and
• Peter J. Rutledge

Beilstein J. Org. Chem. 2015, 11, 2549–2556, doi:10.3762/bjoc.11.275

• ][24][25][26]. Several new developments in the related hetero-Diels–Alder reaction of acylnitroso species have also been reported recently [27][28][29][30]. These methodologies generally involve in situ generation of the acylnitroso species, achieved using a variety of oxidants including vanadium- [28

• trapped by hetero-Diels–Alder reaction with dienes [54][55], and detection of the resulting hetero-Diels–Alder adducts used to confirm the formation of free nitroso intermediates. Thus trapping experiments were conducted using isoprene (14) to investigate the formation of a nitroso species in this

• reaction. First a 1:1 mixture of cycloadducts 15 and 16 was synthesised as a reference sample using Kirby’s conditions for the hetero-Diels–Alder reaction (N-Boc-hydroxylamine (8), isoprene (14) and sodium periodate, Scheme 3a) [54][55]. Then isoprene (14) and N-Boc-hydroxylamine (8) were combined in

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• ester 75. Finally, an elegant cascade reaction involving an aldol condensation, followed by a hetereo Diels–Alder reaction closed the last three rings and antheliolide A (18) was obtained in 74% yield. In summary, the successful total synthesis of antheliolide A proceeded in 25 linear steps with an

Recent highlights in biosynthesis research using stable isotopes

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2015, 11, 2493–2508, doi:10.3762/bjoc.11.271

• group. The energy barrier of a distorted benzene ring would then be compensated by rearomatization in 23 after intramolecular Diels–Alder reaction. This mechanism would involve a 1,2-hydride shift and a nucleophilic attack of water at C-2’. The second discussed route starts with a nucleophilic attack of

• the phenolic oxygen at C-6 to close the macrocycle in 25. In this mechanism, the aromaticity of the phenol ring remains untouched. Intramolecular Diels–Alder reaction gives rise to the hexacyclic system 26, which would then be oxidized to pyrrocidine A (24) at C-2’. In contrast to route A, the

Synthesis of constrained analogues of tryptophan

• Elisabetta Rossi,
• Valentina Pirovano,
• Marco Negrato,
• Giorgio Abbiati and
• Monica Dell’Acqua

Beilstein J. Org. Chem. 2015, 11, 1997–2006, doi:10.3762/bjoc.11.216

• library of compounds bearing the free amino acid function at C-3 and pertaining to the class of constrained tryptophan analogues. Keywords: constrained tryptophans; Diels–Alder; indoles; tetrahydrocarbazoles; unnatural amino acids; Introduction With the term of “unnatural” amino acids, a plethora of

• the substitution pattern of starting materials (substituted arylhydrazines and cyclohexanones) and is therefore useful mainly for the synthesis of symmetrically or unsubstituted derivatives [16][17]. Recently, our research group described the synthesis of tetrahydrocarbazole derivatives by Diels–Alder

• -3-carboxylic acid derivatives 3, constrained analogues of tryptophan, could be synthesized by Diels–Alder reactions between 2-vinylindoles 1 [22] as dienes and methyl 2-acetamidoacrylate (dehydroalanine) 2 [23] as dienophile (Scheme 1). Reported [4 + 2] cycloaddition reactions of methyl 2

Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate

• Piotr Wałejko,
• Michał Dąbrowski,
• Lech Szczepaniak,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 1893–1901, doi:10.3762/bjoc.11.204

• reaction may be improved by using neat reaction conditions. Experimental A mixture of 1 and 2 (1.6:1) is readily available from the Diels–Alder reaction of furan and acrylonitrile according to the literature procedure [28][29]. The pure isomers were isolated by column chromatography. The 1H and 13C NMR

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

• have covered literature that appeared during the last seven years (2008–2014). Keywords: Diels–Alder chemistry; green chemistry; natural products; olefin metathesis; polycycles; ring-rearrangement metathesis; Introduction Transition metal–carbene complexes (Figure 1) introduced during the last two

• aburatubolactam A (113) by using a tandem ROM–RCM sequence as the key step. To this end, the required key building block, the bicyclo[3.3.0]octene ring system 108b has been synthesized by a RRM sequence via catalyst 1 starting with the functionalized bicyclo[2.2.1]heptene system 107. Thus, the Diels–Alder (DA

• ] have demonstrated an intramolecular Diels–Alder (IMDA) reaction followed by a RCM–ROM–CM cascade was found to be useful to assemble a linear triquinane framework. Microwave assisted IMDA reaction of cyclopentadiene derivative 210 performed in chlorobenzene at 201 °C under 310 psi pressure gave the

The simple production of nonsymmetric quaterpyridines through Kröhnke pyridine synthesis

• Isabelle Sasaki,
• Jean-Claude Daran and
• Gérard Commenges

Beilstein J. Org. Chem. 2015, 11, 1781–1785, doi:10.3762/bjoc.11.193

• pathway [17][20], or a Suzuki–Miyaura cross-coupling reaction [21]. The use of triazine derivatives (which under particular conditions undergo an inverse Diels–Alder reaction) can also produce oligopyridines [22]. On the other hand, there are a limited number of reports dealing with the preparation of

Design and synthesis of propellane derivatives and oxa-bowls via ring-rearrangement metathesis as a key step

• Sambasivarao Kotha and
• Rama Gunta

Beilstein J. Org. Chem. 2015, 11, 1727–1731, doi:10.3762/bjoc.11.188

• ] we conceived a new and simple route to propellane derivatives and oxa-bowls [21][22][23][24][25][26]. This strategy starts from simple starting materials and involves a Diels–Alder (DA) reaction [27][28] and RRM as the key steps. Results and Discussion Strategy The retrosynthetic strategy to diverse

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

• quick and economically accessible for developing styelsamine B (4) and cystodytin J (1) bioactive derivatives. Synthesis of sebastianine A (38) and its regioisomer (39) The first step of the sebastianine A synthesis was based on a Diels–Alder reaction between a pyrroloquinone used as the dienophile and

• conditions to give the natural product and its regioisomer (Scheme 2) [59]. The Diels–Alder cyclisation seems to be the key step for sebastianine A synthesis with a very low yield. Recently, the same cycloaddition was successfully performed on related compounds by attaching a bromine atom on the

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

• homogeneous PRC has been showcased by its exploitation in a number of total syntheses. For example, (+)-gliocladin C was synthesized by Stephenson [9], natural product heitziamide A was made by Yoon and co-workers via a PRC Diels−Alder cycloaddition [10], and a Ru(bpy)32+ reaction with an N-(acyloxyl

Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

• Sara J. Krivickas,
• Chiho Hashimoto,
• Junya Yoshida,
• Akira Ueda,
• Kazuyuki Takahashi,
• John D. Wallis and
• Hatsumi Mori

Beilstein J. Org. Chem. 2015, 11, 1561–1569, doi:10.3762/bjoc.11.172

• ]. The trans-alkene 8 was reacted with trithione 7 under standard Diels–Alder cycloaddition conditions in refluxing toluene to afford a mixture of the trans-(S,S)- and (R,R)-9 in 56% yield (Scheme 1). The purchased alkene contained a small amount of the cis-isomer (trans-form:cis-form 96:4), but the cis

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

• Abstract A new tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR) has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of

• linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM–IMDAR protocols. Keywords: bicyclic frameworks; cross enyne metathesis; Diels–Alder

• bonds, expanding the utility of metathesis processes beyond olefinic substrates [8][9]. The inherent tandem nature of enyne metathesis is particularly appealing in its combination with the Diels–Alder reaction. This tandem protocol is well suited for addressing a broad range of complex molecules since

Thermal properties of ruthenium alkylidene-polymerized dicyclopentadiene

• Yuval Vidavsky,
• Yotam Navon,
• Yakov Ginzburg,
• Moshe Gottlieb and
• N. Gabriel Lemcoff

Beilstein J. Org. Chem. 2015, 11, 1469–1474, doi:10.3762/bjoc.11.159

• equilibrates and further ruthenium–alkylidene metathesis with neighboring double bonds may be promoted. Alternatively, thermal decomposition of DCPD (or larger oligomers) to cyclopentadiene (CPD) by a retro-Diels–Alder reaction could also explain the observed phenomenon, although unlikely at room temperature

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

• Karolina Żukowska,
• Eva Pump,
• Aleksandra E. Pazio,
• Krzysztof Woźniak,
• Luigi Cavallo and
• Christian Slugovc

Beilstein J. Org. Chem. 2015, 11, 1458–1468, doi:10.3762/bjoc.11.158

• substrate-induced activation is impeded. This effect turned out to be of particular relevance when the polymerization of dicyclopentadiene is regarded. Because polymerizations were carried out in open reaction vessels, the retro-Diels–Alder reaction of 23, releasing volatile cyclopentadiene, is a concurring

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

• cycloaddition reactions providing indolyl C-deoxyribosides [6], cyclopentenonyl C-deoxyribosides [9], triazolyl C-deoxyribosides [12][13], carboranyl C-deoxyribosides [7], and finally also in Diels–Alder reaction with cyclobutadiene derivatives [8]. Despite of the above mentioned transformations, alkynyl C

Design and synthesis of polycyclic sulfones via Diels–Alder reaction and ring-rearrangement metathesis as key steps

• Sambasivarao Kotha and
• Rama Gunta

Beilstein J. Org. Chem. 2015, 11, 1373–1378, doi:10.3762/bjoc.11.148

• Sambasivarao Kotha Rama Gunta Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai-400 076, India, Fax: 022-25767152 10.3762/bjoc.11.148 Abstract Here, we describe a new and simple synthetic strategy to various polycyclic sulfones via Diels–Alder reaction and ring

• . Interestingly the starting materials used are simple and commercially available. Keywords: alkenylation; Diels–Alder reaction; ring-rearrangement metathesis; sulfones; Introduction Sulfones [1][2][3][4][5][6][7][8] are popular building blocks [9] in organic synthesis. They are also useful substrates for the

• Ramberg–Bäcklund reaction [10] and they can be alkylated via carbanion chemistry. Moreover, they are suitable synthons in Diels–Alder (DA) reactions [11][12][13][14]. In view of various applications of sulfone derivatives, we envisioned a new synthetic strategy based on ring-rearrangement metathesis (RRM

Spiro annulation of cage polycycles via Grignard reaction and ring-closing metathesis as key steps

• Sambasivarao Kotha,
• Mohammad Saifuddin,
• Rashid Ali and
• Gaddamedi Sreevani

Beilstein J. Org. Chem. 2015, 11, 1367–1372, doi:10.3762/bjoc.11.147

• -pyrano cage compound 7 involving ring-closing metathesis is reported. The hexacyclic dione 10 was prepared from simple and readily available starting materials such as 1,4-naphthoquinone and cyclopentadiene. The synthesis of an unprecedented octacyclic cage compound through intramolecular Diels–Alder (DA

• ) reaction as a key step is described. The structures of three new cage compounds 7, 12 and 18 were confirmed by single crystal X-ray diffraction studies. Keywords: cage molecules; Diels–Alder reaction; Grignard reaction; ring-closing metathesis; spirocycles; Introduction Design and synthesis of

• Claisen rearrangement and RCM as key steps [21][30]. Here, we have prepared the cage dione 10 by the known route involving two atom-economic protocols such as Diels–Alder reaction and [2 + 2] photocycloaddition [42][43][44][45] (Scheme 1). Later, the hexacyclic cage dione 10 was subjected to a Grignard