Thiourea-catalyzed Diels–Alder reaction of a naphthoquinone monoketal dienophile

• Carsten S. Kramer and
• Stefan Bräse

Beilstein J. Org. Chem. 2013, 9, 1414–1418, doi:10.3762/bjoc.9.158

• hindered naphthoquinone monoketal dienophile 3 with diene 4. The use of thiourea catalysis allowed for the first time the highly selective synthesis of the exo-product 2a in up to 63% yield. In this reaction a new quaternary center was built. The so formed cycloaddition product 2a represents the ABC

• ][8]. In our recent studies towards a synthetic access to the natural product beticolin 0 (1) [9] (Scheme 1), we have found that naphthoquinone monoketals are suitable building blocks for our designed synthesis [9]. In our retrosynthetic approach, the naphthoquinone monoketal dienophile 3 was found to

• undergo cycloaddition with diene 4 to tricycle 2, which represents the ABC-ring system of beticolin 0 (1) and other beticolins [10]. We found that dienophile 3 and diene 4 can undergo a cycloaddition by applying either thermal conditions or microwave irradiation to these both compounds (Table 1) [9

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• nitroalkenes 5a–c as heterodienes, ethyl vinyl ether (EVE) as a dienophile, and selected electron-deficient alkenes as 1,3-dipolarophiles. The employment of different organic solutions of LiClO4 or LiCl as promoter systems provided the respective nitroso acetals with yields from 34–72% and good levels of

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

• Rajendra K. Jangid,
• Nidhi Sogani,
• Neelima Gupta,
• Raj K. Bansal,
• Moritz von Hopffgarten and
• Gernot Frenking

Beilstein J. Org. Chem. 2013, 9, 392–400, doi:10.3762/bjoc.9.40

• dimerization through a DA reaction [13]. The first DA reaction involving the –C=C–C=P– moiety of phosphinine as a diene was reported by Märkl and Lieb [14], while Mathey and Alcaraz showed that phosphinine could react as a dienophile as well, with the reaction taking place at the >C=P– functionality of

• catalyst In the DA reactions catalysed by excess dialkylaluminium chloride, formation of the chelate complex cation 11 of the dienophile (Scheme 3) has been established experimentally [36][37][38], and the high reactivity of the dienophile in the presence of the organoaluminium catalyst was attributed to

• -phosphaindolizine-η1-P-aluminium(O-menthoxy) dichloride with 2,3-dimethylbutadiene. Formation of the cationic 1:1 complex of the dienophile and dialkylaluminium. Disproportionation of the 1:1 complex of 2-phosphaindolizine and Al(O-menthoxy)Cl2. Attack of 1,3-butadiene on Si and Re faces of >C=P– functionality of 2

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

• ] cycloaddition mode compete [123]. Occasionally highly alkylated bisallenes such as 24 also provide ene-addition products. If the double-bond dienophile is replaced by an activated triple-bond dienophile 173, another course of events is observed (Scheme 42) [21][124][125][126]. In this case the Diels–Alder step

Facile synthesis of functionalized tetrahydroquinolines via domino Povarov reactions of arylamines, methyl propiolate and aromatic aldehydes

• Jing Sun,
• Hong Gao,
• Qun Wu and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2012, 8, 1839–1843, doi:10.3762/bjoc.8.211

• ]. However, a survey of literature reveals that a Povarov reaction with in situ generated β-enamino ester as dienophile has not been reported until now. Recently, Zhu and Masson successfully developed three-component Povarov reactions using enamides as dienophiles leading to a highly efficient synthesis of

• of N-aryl aldimine B as the N-hetero diene with β-enamino ester A as the dienophile may give directly the tetrahydroquinoline 1. At present it is very difficult to distinguish these two reaction paths. It may be due to the fact that the four sequential reactions are all retro equilibrium reactions

• propiolates, and successfully established the imino Diels–Alder reaction with β-enamino ester as dienophile. This reaction provides a convenient and stereoselective procedure for the preparation of 2-aryl-4-arylamino-1,2,3,4-tetrahydroquinoline-3-carboxylates in satisfactory yields. Furthermore, we

Imidazolinium and amidinium salts as Lewis acid organocatalysts

• Oksana Sereda,
• Nicole Clemens,
• Tatjana Heckel and
• René Wilhelm

Beilstein J. Org. Chem. 2012, 8, 1798–1803, doi:10.3762/bjoc.8.205

• [10][16][17]. Taking the soft Lewis acidic character of imidazolinium salts into consideration, we were interested to apply these salts in a Diels–Alder reaction with ethyl crotonthioate as dienophile. Due to the low electronegativity of sulfur it would be difficult to catalyze this reaction with

Highly enantioselective access to cannabinoid-type tricyles by organocatalytic Diels–Alder reactions

• Stefan Bräse,
• Nicole Volz,
• Franziska Gläser and
• Martin Nieger

Beilstein J. Org. Chem. 2012, 8, 1385–1392, doi:10.3762/bjoc.8.160

• MacMillan on various model systems (Figure 3) [37]. The effect of these catalysts is based on the formation of iminium ions by condensation of the dienophile bearing a carbonyl group, with the sterically hindered imidazole catalyst. In this way, one side is shielded and only the other side can be attacked

An easily accessible sulfated saccharide mimetic inhibits in vitro human tumor cell adhesion and angiogenesis of vascular endothelial cells

• Grazia Marano,
• Claas Gronewold,
• Martin Frank,
• Anette Merling,
• Christian Kliem,
• Sandra Sauer,
• Manfred Wiessler,
• Eva Frei and
• Reinhard Schwartz-Albiez

Beilstein J. Org. Chem. 2012, 8, 787–803, doi:10.3762/bjoc.8.89

• because it mimics a furanose but without an optically active center, making the synthesis of defined molecules much easier than on a furanose core. Synthetically it is easily accessible and is a dienophile, which allows attachment of marker molecules in a Diels–Alder reaction, leaving the hydroxy groups

Synthesis of fused tricyclic amines unsubstituted at the ring-junction positions by a cascade condensation, cyclization, cycloaddition then decarbonylation strategy

• Iain Coldham,
• Adam J. M. Burrell,
• Hélène D. S. Guerrand,
• Luke Watson,
• Nathaniel G. Martin and
• Niall Oram

Beilstein J. Org. Chem. 2012, 8, 107–111, doi:10.3762/bjoc.8.11

• glycine in toluene gave the desired tricyclic product 19 as a single stereoisomer. NOESY studies verified the stereochemistry as shown. Only one of the two alkene groups acts as the dienophile, as expected for conformational reasons. This synthesis (six steps from nitrile 3) represents an efficient entry

One-pot Diels–Alder cycloaddition/gold(I)-catalyzed 6-endo-dig cyclization for the synthesis of the complex bicyclo[3.3.1]alkenone framework

• Boubacar Sow,
• Gabriel Bellavance,
• Francis Barabé and
• Louis Barriault

Beilstein J. Org. Chem. 2011, 7, 1007–1013, doi:10.3762/bjoc.7.114

• Diels–Alder reaction/Au(I)-catalyzed 6-endo-dig carbocyclization (Scheme 3). Cycloaddition between diene 12 and dienophile 13 should provide the endo cycloadduct 14, which, in the presence of a gold(I) catalyst, would form the gold complex A. This undergoes a carbocyclization of enol ether [24][25][26

• ). One-pot cycloaddition/cyclization of dienes 19 and 20 (Z/E = 6:1 ca.) with N-phenylmaleimide gave ketones 24 and 26 in 93 and 88% yield, respectively, as the sole diastereomers (Table 1, entries 1 and 3). The use of maleic anhydride as the dienophile also provided the desired products 25 and 27

Synthesis of cross-conjugated trienes by rhodium-catalyzed dimerization of monosubstituted allenes

• Tomoya Miura,
• Tsuneaki Biyajima,
• Takeharu Toyoshima and
• Masahiro Murakami

Beilstein J. Org. Chem. 2011, 7, 578–581, doi:10.3762/bjoc.7.67

• dienophile, in toluene at 0 °C (Scheme 3). The conversion of 3a was complete within 1 h, and after chromatographic isolation, bisadducts 5a and 5a’ were obtained in 75% and 6% yields, respectively. The major bisadduct 5a resulted from initial addition to the more congested diene moiety of 3a (site β). When

• tetracyanoethylene (6, TCNE), which was a less reactive dienophile than 4, was used, [4 + 2] cycloaddition also occurred preferentially at site β, but only once on heating at 60 °C for 24 h. Conclusion In summary, we have developed a new dimerization reaction of monosubstituted allenes catalyzed by a rhodium(I)/dppe

Preparation and NMR spectra of four isomeric diformyl[2.2]paracyclophanes (cyclophanes 66)

• Ina Dix,
• Henning Hopf,
• Thota B. N. Satyanarayana and
• Ludger Ernst

Beilstein J. Org. Chem. 2010, 6, 932–937, doi:10.3762/bjoc.6.104

• four different modes (Scheme 1) [2]. Depending on the amounts and the quality of the solutions containing the tetraene 1 and the dienophile 2, more than 60 g of the dialdehyde mixture 4 can be obtained in a single run, corresponding to maximum yields of 46%. Both starting compounds are very reactive

Synthesis of oxa-bridged derivatives from Diels–Alder bis-adducts of butadiene and 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene

• Faiz Ahmed Khan and
• Karuppasamy Parasuraman

Beilstein J. Org. Chem. 2010, 6, No. 64, doi:10.3762/bjoc.6.64

• employing 1,3-butadiene as bis-dienophile component. Herein we report the synthesis of bis-adducts of 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene and butadiene followed by their transformation to oxa-bridged compounds. The stereochemistry of the diastereomeric products was also unequivocally established

• . Conclusion In conclusion, we have demonstrated that the Diels–Alder reaction between 1 (diene component) and 1,3-butadiene (bis-dienophile component) proceeds via endo-endo addition mode to give a 1:1 mixture of diastereomeric bis-adducts. The diastereomeric bis-adducts were separated and transformed into

One-pot three-component synthesis of quinoxaline and phenazine ring systems using Fischer carbene complexes

• Priyabrata Roy and
• Binay Krishna Ghorai

Beilstein J. Org. Chem. 2010, 6, No. 52, doi:10.3762/bjoc.6.52

• extrusion of water by treatment of 7a with DBU in refluxing toluene, gave the quinoxaline derivative 5a [36]. The stereochemistry of the adduct 7a was assigned as exo based on the chemical shift of HA and HB (<4 ppm) [27]. A similar reaction process using N-methylmaleimide (entry 2) as dienophile led to the

• (Table 1, entry 3). The reaction was also examined with dimethyl maleate as the dienophile (Scheme 3). The reaction of pyrazinyl ketone 1A, carbene complex 2 and dimethyl maleate under the same conditions as previously described afforded the three component coupling product 9A in 40% yield via the

Synthesis of some novel annulated pyrido[2,3-d]pyrimidines via stereoselective intramolecular hetero Diels–Alder reactions of 1-oxa-1,3-butadienes

• Mohit L. Deb and
• Pulak J. Bhuyan

Beilstein J. Org. Chem. 2010, 6, No. 11, doi:10.3762/bjoc.6.11

• of the reactions the cis-annelated products were formed either predominantly or exclusively. As the oxabutadiene is part of a cyclic compound and two carbon atoms to which the dienophile is attached are part of a ring system, the endo-transition state is energetically more favorable than the exo

Preparation and Diels–Alder/cross coupling reactions of a 2-diethanolaminoboron- substituted 1,3-diene

• Liqiong Wang,
• Cynthia S. Day,
• Marcus W. Wright and
• Mark E. Welker

Beilstein J. Org. Chem. 2009, 5, No. 45, doi:10.3762/bjoc.5.45

• –100 °C in a sealed tube in toluene with N-phenylmaleimide to obtain >90% yield of cycloadduct, the diethanolamine boronyl diene 2 reacted with this same dienophile to afford a 98% isolated yield of cyclaooduct 4 after only 15 min at 25 °C! We tried to get more quantitative rate constant data about

• greatly improved regioselectivities (Table 1). Whereas the BF3 diene required 36 h of heating to 95–100 °C in a sealed tube in ethanol to provide a 3.3:1 mixture of regioisomers from reaction with ethyl acrylate, the diethanolamine boronyl diene 2 reacted with this same dienophile at reflux for 6 h to

The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid

• Ishmael B. Masesane,
• Andrei S. Batsanov,
• Judith A. K. Howard,
• Raju Mondal and
• Patrick G. Steel

Beilstein J. Org. Chem. 2006, 2, No. 9, doi:10.1186/1860-5397-2-9

• batches, Scheme 1. Whilst this dienophile reacts with considerable regiocontrol (dominated by the nitro group) the stereoselectivity (endo:exo ratio) observed is frequently minimal. [13][14][15] Subjection of nitroacrylate 1 to cycloaddition reaction with furan in CHCl3 at room temperature gave a 2:1

High stereoselectivity on low temperature Diels- Alder reactions

• Luiz Carlos da Silva Filho,
• Valdemar Lacerda Júnior,
• Mauricio Gomes Constantino,
• Gil Valdo José da Silva and
• Paulo Roberto Invernize

Beilstein J. Org. Chem. 2005, 1, No. 14, doi:10.1186/1860-5397-1-14

• : -78°C, room temperature, or under reflux. Excess of diene (cyclopentadiene) was used in each experiment (5 eq.), while the molar ratio dienophile/NbCl5 was maintained constant at 1.0/0.5. The results obtained in these studies are summarized in Table 1 All products were isolated and characterized by