- (2+4)-Cycloaddition with singlet oxygen. 17O-investigation of the reactivity of furfuryl alcohol endoperoxide
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In earlier work, the use of furfuryl alcohol as a specific singlet oxygen acceptor was proposed because of the high ratio between the rate constants of chemical reaction and physical quenching. In contrast to furfuryl aldehyde, a number of products are formed by this type II photooxidation of furfuryl alcohol. These products may be derived from the endoperoxide of furfuryl alcohol as a common intermediate. The present work focuses on the reactivity of this endoperoxide that was marked specifically by the use of 17O2 as a source for singlet oxygen. The analyses of the stable products, their yields and their labeling distribution reveal a strong solvent effect on the primary reaction pathways, and nucleophilic substitution reactions leading to hydroperoxide intermediates are dominant.
- Braun, André M.,Dann, Hans,Gassmann, Ernst,Gerothanassis, Ioannis,Jakob, Laurent,Kateva, Jordanka,Martinez, Claudia G.,Oliveros, Esther
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- Total synthesis of a novel oxa-bowl natural product paracaseolide A via a 'putative' biomimetic pathway
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A total synthesis of bioactive tetracyclic natural product paracaseolide A, embodying an architecturally unusual oxa-bowl framework, has been accomplished from commercially available 5-methyl-2-furfural. The key step involving a thermal [4+2]-dimerization of an appropriately crafted 5-methyl-3- alkenylbutenolide is shown to proceed in a stepwise manner.
- Vasamsetty, Laxmaiah,Khan, Faiz Ahmed,Mehta, Goverdhan
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- Total synthesis of novel bioactive natural product paracaseolide A and analogues: Computational evaluation of a 'proposed' biomimetic Diels-Alder reaction
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A short and generally applicable synthesis of bioactive tetracyclic natural product paracaseolide A has been accomplished employing a 'proposed' biomimetic Diels-Alder reaction as the key strategic step. The Diels-Alder precursors for this purpose were readily assembled through a versatile Suzuki coupling on preformed α-halo butenolides. The mechanistic aspects of the 'putative' biomimetic Diels-Alder reaction have been probed using computational methods, which suggest that this [4+2]-cycloaddition proceeds through a step-wise process and product profile is thermodynamically governed.
- Vasamsetty, Laxmaiah,Sahu, Debashis,Ganguly, Bishwajit,Khan, Faiz Ahmed,Mehta, Goverdhan
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- ANOMALOUS OZONOLYSIS PRODUCTS IN THE ADDITION OF SINGLET OXYGEN TO METHOXYMETHYLFURANS
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The rearrangement of cyclobutadiene ozonides, related to "anomalous ozonolysis", has been elucidated.
- Feringa, Ben L.,Butselaar, Robert J.
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- PSEUDOESTERES Y DERIVADOS XXXIII. SINTESIS DE COMPUESTOS CICLOPROPANICOS POR FOTOLISIS DE PIRAZOLINAS OBTENIDAS POR CICLOADICION 1,3-DIPOLAR A LA 5-METOXI-2(5H)-FURANONA
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By cycloaddition of 2-diazopropane to 5-methoxy-2(5H)-furanone (1) two regioisomeric 1-pyrazolines 3 and 4 are stereospecifically obtained.Both isomers give by photolysis, as major or sole compound, the same cyclopropane derivative 7.Hydrolysis of the bicyclic compound 7, followed by esterification, leads to cis open chain derivatives, which are appropiately functionalized for the synthesis of pyrethroids. a similar set of reactions, using diazomethane-d2 as dipolarophile, affords selectively deuterated cyclopropane derivatives.Palabras clave: Cicloadicion 1,3-dipolar, pirazolinas, fotolisis, ciclopropanos, piretroides.
- Farina, F.,Martin, M. V.,Soria, M. L.
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- AN EFFICIENT PHOTOREACTOR FOR USE OF LINEAR POLYMERIC PHOTOSENSITIZERS WITH PREPARATIVE PURPOSES
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A photoreactor specially designed for preparative synthesis in homogeneous phase employing linear polymeric photosensitizers is described.The reactor allows the direct separation and subsequent reuse of the sensitizer by in situ ultrafiltration of the irradiated solution.The photo-oxidation with visible light of furfural, using as polymeric photosensitizer Rose Bengal covalently bound to linear polystyrene, has been chosen for the evaluation of the reactor as well as for the study of the behaviour of this particular photosensitizer when it is repeatedly used.The results of consecutive identical photo-oxidations indicate that, under the experimental conditions used, this sensitizer is photostable and its efficiency remains constant. Key words: Photoreactors, Photooxidations, Furfural, Polymeric photosensitizers.
- Amat-Guerri, F.,Botija, J. M.,Sastre, R.
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p. 507 - 510
(2007/10/02)
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- Asymmetric 1,3-dipolar cycloadditions to 5-(R)-menthyloxy-2(5H)-furanone
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Various diazo compounds, nitrile oxides, nitrones and azomethine ylides were examined in 1,3-dipolar cycloadditions to enantiomerically pure 5-(R)-menthyloxy-2(5H)-furanone 1a. Pyrazoline 9 was obtained in 100% c.y. as a mixture of 2 diastereoisomers in ratios up to 72:28, whereas pyrazoline 16 was obtained in 100% c.y. as a single enantiomer. Photochemically pyrazolines 9 and 10 have been converted to cyclopropanes 11 and 13. Under thermal conditions pyrazoline 9 is converted to 4-methyl-5-menthyloxy-2(5H)-furanone. Isoxazoles 21a-24a were obtained enantiomerically pure via nitrile oxide addition to 1a in 64-67% yield. Nitrone addition afforded isoxazolidines 27, 28 and 34 with complete anti-facial- and regiochemistry, but with endo-exo-selectivities up to 76%. Enantiomerically pure isoxazolidines were obtained in 25-75% yield. Pyrrolidine 36 was obtained diastereomerically pure in 81% c.y. Pyrrolidines 42 and 45, however, were obtained as diastereomeric mixtures in 37% resp. 6% yield.
- Rispens,Keller,De Lange,Zijlstra,Feringa
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p. 607 - 624
(2007/10/02)
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- Asymmetric Diels-Alder Reactions with 5-Menthyloxy-2(5H)-furanone
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A new class of chiral dienophiles, 5-alkoxy-2(5H)-furanones, has been developed.Both enantiomers of 5-menthyloxy-2(5H)-furanone are readily available in enantiomerically pure form, starting from furfural and d- or l-menthol.Excellent diastereoselectivities (d.e. 99percent) are obtained in thermal Diels-Alder reactions with several cyclic and acyclic dienes.The use of silyl dienol ethers has resulted in new routes to enantiomerically pure cyclohexanones in a highly regioselective manner.
- Jong, Johannes C. de,Bolhuis, Fre van,Feringa, Ben L.
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p. 1247 - 1262
(2007/10/02)
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- 2,3,6-Trioxyfulvenes. Part 1. Synthesis of 1,4-Disubstituted-2,3,6-trioxyfulvenes.
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A new strategy for the construction of the fulvene skeleton from acyclic precursors has been developed.The products obtained show three hydroxyl groups at C(2), C(3), and C(6), and two electron-withdrawing groups R (R = CO2Me, CN, NO2, and SO2-C6H4-p-Me) at C(1) and C(4).The keto-enol tautomerism of these compounds is discussed.The enol forms are maintained as methyl ethers.
- Victory, Pedro,Alvarez-Larena, Angel,Barbera, Eduardo,Batllori, Xavier,Borrell, Jose I.,Cordoba, Carlos
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p. 631 - 674
(2007/10/02)
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- ASYMMETRIC 1,4-ADDITIONS TO 5-ALKOXY-2(5H)-FURANONES. AN EFFICIENT SYNTHESIS OF (R)- AND (S)-3,4-EPOXY-1-BUTANOL
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The synthesis of enantiomerically pure 5-menthyloxy-2(5H)-furanones is described as well as the diastereoselective 1,4-addition of thiols to these butenolides to yield new homochiral C4-synthons.Kinetic resolution of 5-methoxy-2(5H)-furanone, with an enantiomeric excess of 13percent, was achieved by cinchonidine catalysed thiophenol addition. The synthetic utility of the asymmetric thiol additions is illustrated in an efficient route to enantiomerically pure (R)- and (S)-3,4-epoxy-1-butanol.
- Feringa, Ben L.,Lange, Ben De
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p. 7213 - 7222
(2007/10/02)
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- PSEUDOESTERS AND DERIVATIVES. XXIII. REACTION OF 3-BROMO-5-METHOXYFURAN-2(5H)-ONE WITH NUCLEOPHILES. FORMATION OF CYCLOPROPANE DERIVATIVES.
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The reactions of 3-bromo-5-methoxyfuran-2(5H)-one (1) with nucleophiles in acetonitrile, in the presence of potassium carbonate and tetrabutylammonium bromide as a catalyst, are reported.The bromofuranone 1 reacts with several carbon and oxygen nucleophiles to give the cyclopropane bis-lactones 7, 8, 11 or 12.When 1 is reacted with diethylamine or propane-2-thiol in a 2:1 ratio, similar cyclopropane bis-lactones 16 or 21, respectively, are formed.This behaviour is explained on the basis of a mechanism involving a double Michael addition, followed by ring closure via internal nucleophilic substitution of the halogen.
- Farina, Francisco,Maestro, M. Carmen,Martin, M. Rosario,Martin, M. Victoria,Sanchez, Felix,Soria, M. Luisa
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p. 3715 - 3722
(2007/10/02)
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- SENSITIZED PHOTOOXIDATION OF 2-FURFURYL BENZOATE IN METHANOL
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Sensitized photooxidation of 2-furfuryl benzoate in methanol gave eight products.The mechanism for their formations are discussed.
- Kuo, Yueh-Hsiung,Shih, Kae-Shyang
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p. 1361 - 1366
(2007/10/02)
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- SINGLET OXYGEN PHOTOOXYGENATION OF FURANS. ISOLATION AND REACTIONS OF (4+2)-CYCLOADDITION PRODUCTS (UNSATURATED SEC.-OZONIDES)
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Tetraphenylporphin-photosensitized oxygenations of furan (19), 2-methylfuran (26), 2-ethylfuran (39), furfurylalcohol (24), 2-acetylfuran (40), 2-methoxyfuran (42), 2,5-dimethylfuran (30), furfural (25) and 5-methylfurfural (41) in non-polar aprotic solvents yield the corresponding monomeric unsaturated secondary ozonides due to a (4+2)-cycloaddition of singlet oxygen to these furans.With the exception of the ozonide derived from 25, the ozonides were isolated and characterized (1H- and 13NMR spectra, etc.).In non-polar aprotic solvents, the ozonides derived from 19, 26 and 39 undergo thermal rearrangements to the corresponding cis-diepoxides and epoxylactones.Ozonide 31, derived from 30, however, dimerizes; only above about 60 deg is a cis-diepoxide formed from either 31 or its dimer.Rose bengal-photosensitized oxygenations of the furans in alcohols (MeOH, EtOH, i-PrOH) also produce the corresponding ozonides as the primary products of (4+2)-cycloadditions of singlet oxygen to these furans.However, reactions of the alcohols with the ozonides are too fast to allow the ozonides to be isolated.Instead, the same products are obtained as are isolated from reactions carried out by dissolving the ozonides in the alcohols.Depending on the structure of the ozonide, three pathways are available to ozonide/alcohol (ROH) interactions: (1) addition of ROH to yield alkoxy hydroperoxides; one out of several possible isomers is formed in a completely stereoselective and regiospecific reaction; (2) elimination of a bridgehead proton by ROH as a base, as observed with the ozonide derived from 19 to give hydroxy butenolide (78) in yields between 20 and 60percent; and (3) ROH-attack on a carbonyl side-chain under elimination of the corresponding alkyl ester, as observed with furfural photooxygenation which yielded hydroxy butenolide (78) in high yields (>95percent).Interaction of ozonide 31 with tert.-butyl alcohol (t-BuOH) yields quantitatively cis-3-oxo-1-butenylacetate (81) by a Baeyer-Villiger-type rearrangement with vinyl group migration.Hydrogen-bonding between the alcohol and the peroxy group of the ozonides assist the heterolysis of the C-O bonds in the ozonides; the most stabilized cation develops.Front-attack of ROH on this cation explains the stereoselectivity as well as the regiospecificity of the alkoxy hydroperoxide formation; with a bulky alcohol like t-BuOH, ROH-attack on the cation is sterically hindered thus allowing a rearangement to occur. 1,3-Dipolar cycloaddition of p-nitrophenyl azide to ozonide 31 proceeds stereoselectively to one of the isomers 87a/87b.Finally, kinetic results of furan photooxygenation in methanol show the following order of furan-reactivity towards singlet oxygen: 30> 42> 26> 19> 41> 25, with absolute rate constants ranging from 1.8E8(with 30)to 8.4E4 M-1 s-1 (with 25).
- Gollnick, Klaus,Griesbeck, Axel
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p. 2057 - 2068
(2007/10/02)
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- On the Knowledge of the Catalytic Dimerization of Acrylic Acid Derivatives by Palladium Complexes. III. Reactions of β-Palladio Acrylates and Their Relation to the Catalytic Reaction
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Complexes of the type L2PdCl(CH=CHCOOCH3) (L2 = 2PPh3 or Ph2PCH2CH2PPh2) were decomposed to dimethyl muconate by pyrolysis or by substraction of the phosphine ligands with (CH3CN)2PdCl2 in acetonitrile.The last mentioned reaction gave Δ3-dimethyl dihydromuconate in the presence of hydrochloric acid. Δ3-Dimethyl dihydromuconate was also formed by decomposition of (Ph2PCH2CH2PPh2)PdCl(CH=CHCOOCH3) with HBF4 in acetonitrile, but the analogous reaction in methyl acrylate as solvent gave Δ2-dimetyl dihydromuconate.Thus, we have simulated the formation of the two m ain products of the catalytic dimerization of methyl acrylate with palladium(II)chloride in a stoichiometric manner.Mechanisms with hydride and carbene intermediates are discussed.
- Oehme, G.,Pracejus, H.
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p. 798 - 808
(2007/10/02)
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