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