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

• yield. Ruthenium catalyzed oxidation of the bis-adducts followed by a one-pot transformation of the resulting α-diketone furnished oxa-bridged compounds. Unambiguous stereochemical assignments of both diastereomeric series are reported. Keywords: Diels–Alder reactions; diketones; oxa-bridged

• derivatives; ruthenium; 3-sulfolene; Introduction 3-Sulfolene is a nonflammable, nontoxic, nonhygroscopic and stable crystalline solid and is a convenient equivalent for gaseous 1,3-butadiene [1][2][3] and is commonly used for in situ generation of 1,3-butadiene as the diene component in Diels–Alder

• reactions. We and other groups have demonstrated the utility of cyclic dienes for the synthesis of 2:1 Diels–Alder bis-adducts with 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene 1 [4][5][6][7]. In the case of cyclic dienes (or trienes) such as cyclohexa-1,4-diene and cycloheptatriene, endo-syn-endo

Synthesis of fluorinated δ-lactams via cycloisomerization of gem-difluoropropargyl amides

• Satoru Arimitsu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2010, 6, No. 48, doi:10.3762/bjoc.6.48

• some bioactive compounds [23][24][25]. Dienes 2a and 2b were used in Diels–Alder reactions with 4 and 6 to produce 5 and 4,4-difluoroisoquinolin-3-one derivatives 7, respectively, in excellent yield and good stereoselectivity (Scheme 1). Phenyl-substituted diene 2c gave no reaction, even after a longer

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Novel loop-like aromatic compounds: a further step on the road to nanobelts and nanotubes

• Venkataramana Rajuri,
• Dariush Ajami,
• Gaston R. Schaller,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2010, 6, No. 30, doi:10.3762/bjoc.6.30

• the most electron deficient dienes used in Diels–Alder reactions and is readily accessible by the reaction of tetrachlorothiophene with peroxytrifluoroacetic acid [24][25]. The Diels–Alder reaction of 1 with an excess of diene 10, followed by instantaneous elimination of sulfur dioxide furnished

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

• Diels–Alder reactions involving 1-oxa-1,3-butadienes. Keywords: β-halo aldehydes; hetero Diels–Alder reaction; 1-oxa-1,3-butadiene; pyrido[2,3-d]pyrimidines; uracil; Introduction The importance of uracil and its annulated derivatives is well recognized by synthetic as well as biological chemists [1][2

• preparation of these complex molecules. However, there still remains many challenges in the synthesis of these naturally occurring complex molecules [22][23][24][25][26][27][28][29][30][31]. Hetero Diels–Alder reactions [32][33][34][35] are becoming a mainstay of heterocyclic and natural product synthesis

• complex annulated pyrido[2,3-d]pyrimidines by intramolecular hetero Diels–Alder reactions involving 1-oxa-1,3-butadienes (Scheme 1). The key intermediate, the 2-chloro-3-formyl uracil derivative 1 (β-halo aldehyde), was prepared by the reaction of N,N-dimethyl barbituric acid with Vielsmeier reagent (DMF

Solvent-free phase-vanishing reactions with PTFE (Teflon^®) as a phase screen

• Kevin Pels and
• Veljko Dragojlovic

Beilstein J. Org. Chem. 2009, 5, No. 75, doi:10.3762/bjoc.5.75

• and either acrylic acid or dimethyl fumarate react at a relatively high rate [26]. As most Diels-Alder reactions are relatively slow, and most dienes are highly reactive towards halogens, it may be necessary to carry out sequential reactions. Solvent-free PV-PTFE reaction design is simple and

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

• and Diels–Alder reactions of pyridine cobaloxime dienyl complexes over 15 years ago. Since that time, we have reported a number of synthetic routes to these and other related types of cobalt dienyl complexes as well as their subsequent cycloaddition and demetallation chemistry [3][4][5], and other

• boronyl diene 2. This diethanolamine boronyl diene 2 has proved to be significantly more reactive and more regioselective in Diels–Alder reactions compared to its BF3 diene counterpart (Table 1, Scheme 2) [8]. Qualitatively, we initially noticed that whereas the BF3 diene required 16 h of heating at 95

• regioselectivities observed in the original Diels–Alder reactions were maintained after cross coupling. Conclusion In conclusion, we report a simple preparation of a 2-boronyl substituted 1,3 diene which has proved to be the most reactive 2-main group element or 2-transition metal element substituted diene for Diels

Synthesis of rigidified flavin–guanidinium ion conjugates and investigation of their photocatalytic properties

• Harald Schmaderer,
• Mouchumi Bhuyan and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 26, doi:10.3762/bjoc.5.26

• presence of the anions did not induce significant changes of the emission properties suggesting affinity constants smaller than 103 L/mol. Photo Diels–Alder reactions in the presence of a sensitizer and light have been described [59][60][61][62][63][64]. Therefore flavins 1 and 2 were tested as catalyst

• benzyl ether cleavage, nitro arene reductions and Diels–Alder reactions. However, no significant gain in photocatalytic performance by the guanidinium ion substrate binding site was observed in comparison to flavins lacking the binding site and the rigid Kemp’s acid skeleton. The primary interaction

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• , which envisions the preparation of fragments 19 and 20 from the optical isomers of oxodicyclopentadiene 21 [26][27]. Thus, iodide 19 prepared from compound (+)-21 would be coupled with nitrile 20, obtained from (−)-21. Sordaricin (2) would be completed by retro- and normal Diels-Alder reactions. The

Phase- vanishing halolactonization of neat substrates

• Nicole Windmon and
• Veljko Dragojlovic

Beilstein J. Org. Chem. 2008, 4, No. 29, doi:10.3762/bjoc.4.29

• . Compounds 7, 17 and 20 were prepared in Diels-Alder reactions between cyclopentadiene and the corresponding dienophiles. Diacid 14 was prepared in a reaction between cyclopentadiene and maleic anhydride followed by aqueous hydrolysis. Those compounds gave satisfactory GC-MS and 1H NMR spectra. Reactions

Diels- Alder reactions using 4,7-dioxygenated indanones as dienophiles for regioselective construction of oxygenated 2,3-dihydrobenz[f]indenone skeleton

• Natsuno Etomi,
• Takuya Kumamoto,
• Waka Nakanishi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2008, 4, No. 15, doi:10.3762/bjoc.4.15

• , key intermediates for the synthesis of kinamycin antibiotics, was achieved via Diels-Alder reactions (DAR) using 4,7-dioxygenated indanone-type compounds as dienophiles. Reaction of indanetrione with 1-methoxybutadiene gave a 1 : 1 mixture of undesired 4,5,9-trioxygenated 2,3-dihydrobenz[f]indenone

Asymmetric aza-Diels- Alder reaction of Danishefsky's diene with imines in a chiral reaction medium

• Bruce Pégot,
• Olivier Nguyen Van Buu,
• Didier Gori and
• Giang Vo-Thanh

Beilstein J. Org. Chem. 2006, 2, No. 18, doi:10.1186/1860-5397-2-18

• efficiency is preserved. Background Aza-Diels-Alder reactions rank among the most efficient method for the construction of nitrogen-containing six-membered ring compounds.[1] The reaction of Danishefsky's diene 1 with imine 2 provides a convenient protocol for the synthesis of 2-substituted-2,3-dihydro-4

• ] Encouraged by this result, we decided to develop asymmetric aza-Diels-Alder reactions of chiral imines with Danishefsky's diene using a chiral ionic liquid as a chiral reaction medium. In our initial studies, we attempt to optimize the conditions for the aza-Diels-Alder reaction between Danishefsky's diene 1

• solvent-free microwave activation. All aza-Diels-Alder reactions were performed under argon at room temperature without either a Lewis acid catalyst or organic solvent (Table 1). As illustrated in Table 1, both yield and diastereoselectivity are highest when performing the experiment with 2 equivalents of

An efficient synthesis of novel pyrano[2,3-d]- and furopyrano[2,3-d]pyrimidines via indium- catalyzed multi- component domino reaction

• Dipak Prajapati and
• Mukut Gohain

Beilstein J. Org. Chem. 2006, 2, No. 11, doi:10.1186/1860-5397-2-11

• Mukaiyama Aldol reactions, Friedel-Crafts acylations,[6] Pavarob reactions[7] and Diels-Alder reactions[8] in water. Since the work of Loh,[8] indium halide has also been shown to be an effective Lewis acid catalyst for various reactions in aqueous media. [9][10] However, its use in the hetero Diels-Alder

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• ] (Scheme 4) and to the related photoinduced bicyclization observed by Nakatani and Saito[9] (Scheme 5). Since suspected intermediate A proved too reactive to isolate, we sought to trap it with DMAD through Diels-Alder reactions with the isobenzofuran units. Acetylene 1 was dissolved in neat DMAD and the

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

• catalyzed Diels-Alder reactions [15]. Cycloenones usually do not react with cyclopentadiene in absence of a Lewis acid. In our previous exploratory experiments we have demonstrated that niobium pentachloride promotes Diels-Alder reaction, in ethyl acetate solution, between 2-cyclohexenone (2) and

• -cycloenones 2, 3 and 5 with literature data using other Lewis acids. The possibility of effecting Diels-Alder reactions at -78°C with some substrates is, in our opinion, the most important aspect: besides demonstrating the strong activation of the 2-cycloenones system exerted by NbCl5, it results in the

• NbCl5 has proved to be a promising tool for Diels-Alder reactions between 2-cycloenones and cyclopentadiene. As compared to other Lewis acids, it is more effective, giving higher stereoselectivity, good yields and requiring lower reaction times and temperatures. Experimental section Preparation of