Cycloadditionen von 3,4-Dimethoxyfuran an Dienophile

On cycloaddition reactions with 3,4-dimethoxyfuran We describe new cycloadditions of 3,4-dimethoxyfuran (3,4-DF, 1 ) with various dienophiles. In contrast to furan, the reaction of 3,4-DF with maleic anhydride gives exo- and endo-adducts at approximately the same rate. The thermodynamically more stable product is again the exo-product. Less active dienophiles lead also to mixtures of exo- and endo-adducts, except for citraconic anhydride (methylmaleic anhydride) which forms only the adduct with an endo-methyl group. Dimethylmaleic anhydride could not be reacted with 3,4-DF. All adducts with 3,4-DF contain a hidden 1,2-dicarbonyl group in the form of an endiolether. Its pronounced nucleophilic character allows a series of further additions. Noteworthy are the stereospecific cis-additions of halogens and the preparation of several acetals. Ozonolysis of the enolether in 4 allows the preparation of the hitherto unknown 2r, 3trans, 4trans, 5cis-tetrahydrofuran tetracarboxylic acid and derivatives thereof ( 5 and 6 ).     

Cycloadditionen von 3,4-Dimethoxyfuran an Benzochinone

Cycloadditions of 3,4-dimethoxyfuran with benzoquinones Cycloaddition of 3,4-dimethoxyfuran (3,4-DF, 1 ) with 1,4-benzoquinones furnishes isolable (2 + 4)-adducts in high yield. The crystalline products with benzoquinone, 2-methyl-benzoquinone, 2,3-dimethoxy-benzoquinone have endo-configuration, whereas 2,3-dimethyl-benzoquinone gives the exo-adduct 4c exclusively. Halogens (Cl₂, Br₂) add rapidly across the highly nucleophilic double bond of 3 or 4 in stereospecific cis-manner, and exclusively from the exo-side. The product 5c shows no sign of enolization to the hydroquinone; but with 3a and 3d the hydroquinones 6 were found. Methanolysis of 5 leads to the stable acetals 7 and 8 . On oxidation of the hydroquinones 7 the thermolabile quinones 10 were obtained. Preparative pyrolysis of 10a under relatively mild conditions (N₂, 200°, 0.1 Torr) gives tetramethoxy ethene ( 11 ) and isobenzofuran-4,7-quinone 12 , a yellowish, crystalline and stable compound.     

3,4-Dimethoxyfuran: Eigenschaften,Berechnungen und Substitutionsreaktionen

3,4-Dimethoxyfuran: Properties, Calculations and some Substitution Reactions 3,4-Dimethoxyfuran (3,4-DF) is much more reactive than furan itself. We present experimental details for the synthesis of this useful compound in 50–100 g batches. 3-4-Dibenzyloxyfuran has also been prepared. Quantum mechanical calculations by PPP-and CNDO-methods analogous to furan itself gave the following information (compared with furan): enhanced negative partial charge at C(2) and C(5), higher acidity at α-position, a stronger and at the same time inverted dipol moment. In accordance with the calculations, 3,4-DF can easily be substituted by weak electrophilic reagents, e.g. in a typical Mannich reaction. The bis-amino compound 8 is produced in good yields. Lithiation by butyl-Li leads to mono- or di-substituted products. The mono- and di-Li-3,4-DF have been used for the preparation of various acylated and alkylated 3,4-DF derivatives. By acid hydrolysis of 3,4-DF crystalline 4-methoxy-3 (2H)-furanone has been prepared.     

Cycloaddition of 3,4-Dimethoxyfuran with 1,4-Benzoquinones under High Pressure

High-pressure cycloaddition of 3,4-dimethoxyfuran with 1,4-benzoquinone, toluquinone and 2,3-dimethoxy-1,4-benzoquinone show, at 7 kbar and room temperature, prevailing formation of endo-isomers. Raising pressure (or temperature) results in a surprising increase of the exo-isomer. By catalytic hydrogenation of a mixture 3a/4a , followed by chromatography, the pure diastereomers 5 and 6 were obtained.     

Favorskii-Umlagerung in Gegenwart von 3,4-Dimethoxyfuran: 11endo-oxa-tricyclo [4.3.1.12,5]undec-3-en-10-on und Derivate

Favorskii -rearrangement in the presence of 3,4-dimethoxyfuran: preparation of 3,4-dimethoxy 11 endo -oxo-tricyclo [4.3.1.1^2,5]undec-3-en-10-one and any derivatives On treatment with sodiumhydride of 2-chloro-cyclohexanone in the presence of 3,4-dimethoxyfuran, a possible intermediate of the Favorskii-rearrangement has been trapped as 3,4-dimethoxy-11endo-oxa-tricyclo [4.3.1.1^2,5]undec-3-en-10-one ( 3 ). This new compound contains a highly nucleophilic double bond. It can be cleaved in high yield by ozonolysis to 2exo, 4exo-bis (methoxycarbonyl)-3-oxabicyclo [3.3.1]nonan-9-one ( 4 ). Addition of chlorine to 3 occurs in stereoselective exo-cis-manner to the crystalline 3exo, 4exo-dichloro-3endo,4endo-dimethoxy 11endo-oxa-tricyclo [4.3.1.1^2,5]undecan-10-one ( 5 ). Silver ion assisted hydrolysis of 5 , followed by thermal treatment of the intermediate hydrates, leads to the red 11endo-oxa-tricyclo [4.3.1.1^2,5]undecan-3,4, 10-trione ( 6 ), and methanolysis to 3,3,4,4-tetramethoxy-11endo-oxa-tricyclo [4.3.1.1^2,5]undecan-10-one ( 8 ). By photolytic decarbonylation, 8 is converted into 3,3,4,4-tetramethoxy-10-oxa-tricyclo-[4.3.1^2,5.0]decan ( 9 ).     

Rhodium (I)-katalysierte Reaktionen der [2+4]-Cycloaddukte aus 3,4-Dimethoxyfuran und Acetylendicarbonsäure-estern

[2+4]-Cycloaddition Products of 3,4-Dimethoxyfuran with Acetylenedicarboxylates and Their Transformations under the Influence of Rhodium(I) Catalysts 3,4-Dimethoxyfuran ( 1 ) readily reacts with acetylenedicarboxylates ( 2 ) at room temperature in a [2+4]-cycloaddition to give a mono-( 3 ) and several di-addition products. 90% of the latter consists of the endo-exo compound 4 . Under the influence of catalytic amounts of [Rh(CO)₂Cl]₂ the mixture of mono- and di-adducts in methanolic solution is smoothly transformed into endo-5,5,6-trimethoxy-7-oxabicyclo [2.2.1]hept-2-ene-2,3-dicarboxylate

1 Alle Verbindungen sind racemisch. Die Formeln stellen jeweils nur ein Enantiomeres dar.

(5) , 3-hydroxy-4,5-dimethoxyphthalate ( 6 ) and (I R *, 2 S *, 4 R *, 5 R *, 7 R *, 11 R *, 12 R *) -5,8,8,9,12-pentamethoxy-3,6-dioxatetracyclo [5.3.1.1 ^2,5 . 0 ^4,11 ]dodec-9-ene-1,11-dicarboxylate ( 7 ).     

Construction of an Octahydropyrido[3,4-b]carbazole Skeleton

Russian Journal of Organic Chemistry - The octahydropyridocarbazole skeleton is an important key structure for the synthesis of pyridocarbazole alkaloids, including the antineoplastic agent...     

聚乙撑二氧噻吩阳极降解的研究

研究了聚乙撑二氧噻吩(PEDOT)膜在水溶液中的阳极降解过程. 研究发现PEDOT的阳极过程可以分为p掺杂区[电位范围－0.3～0.5 V (相对于饱和甘汞电极; vs. SCE)]、过渡区[电位范围0.6～1 V (vs. SCE)]、过氧化区[电位范围1.2～1.6 V (vs. SCE)]三个电位区域. 用电化学阻抗谱法、循环伏安法、红外光谱技术、膜电阻测量以及电子自旋共振技术分别研究了PEDOT膜在这三个电位区域的行为. 结果表明: PEDOT膜在这三个电位区域的性质有明显不同. 在p掺杂区PEDOT膜的官能团、共轭结构、导电性均保持, 即在这个电位区发生可逆的掺杂/脱掺杂反应, 膜几乎不降解. 在过渡区和过氧化区, PEDOT膜均发生了降解. 与传统的导电聚合物在高电位的阳极降解的过氧化过程不同, 我们认为膜在较高电位(过渡区)发生一个驰豫过程, 该过程使得膜的官能团改变, 但是膜的共轭结构和导电性均保持; 而在更高的电位区(过氧化区)膜的降解和一般意义的过氧化降解相同, 此时膜的官能团、共轭结构、导电性均发生不可逆的破坏.     

3,4-Diaminocoumarins

A number of 3,4-diaminocoumarins was obtained by hydrogenation of 3-nitro-4-aminocoumarins. It was established that these compounds exist in the coumarin form, and monoacetylation of the 3-NH₂ group does not shift the tautomeric equilibrium.See [1] for a previous communication.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 316–320, March, 1976.     

Asymmetric synthesis of trans-3,4-dialkyl-gamma-butyrolactones via an acyl-Claisen and iodolactonization route

[reaction: see text] A new, efficient, and general asymmetric synthesis of enantiomerically pure trans-3,4-dialkyl-gamma-lactones has been developed. The key steps are (1) copper-catalyzed three-component coupling of chiral amine, aldehyde, and alkyne, (2) acyl-Claisen rearrangement, and (3) iodolactonization. The products, chiral gamma-lactones, are versatile synthetic intermediates and structural units of natural products and modified nucleosides.     

Facile synthesis of 4-substituted 3,4-dihydrocoumarins via an organocatalytic double decarboxylation process

3,4-Dihydrocoumarins, considered to be valuable building blocks, have attracted considerable attention due to their various biological activities. Herein, we have documented an efficient and convenient double decarboxylation process for the synthesis of 4-substituted 3,4-dihydrocoumarin in moderate to excellent yields under mild reaction conditions (up to 98%).     

Structure of 3,4-dinitro-3,4-dimethyl-1,1-diphenyl-1-silacyclopentane

Conclusions 3,4-Dinitro-3,4-dimethyl-1,1-diphenyl-1-silacyclopentane in the liquid phase has a half-chair conformation, and in the solid phase, its conformation is described by a form intermediate between the half-chair and the envelope conformation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2731–2736, December, 1985.     

A nucleophilic 1,3-rearrangement leading to 3,4-disubstituted 3,4-dihydroquinolines

A new nucleophilic 1,3-rearrangement is observed when treating 2-methoxyquinolino-3-lithium with an α-C substituted deoxybenzoin,and this rearrangement yielded an unusual 3,4-disubstituted 3,4-dihydroquinoline.Several similar reactions were designed and executed to investigate this novel 1,3-rearrangement,and a mechanism involving a nucleophilic addition and a following 1,3-rearrangement with an unusual dearomatization on the quinoline ring is proposed.     

Efficient synthesis of cis- and trans-3,4-dihydroxy-3,4-dihydromollugin

An efficient synthesis of naturally occurring compounds isolated from Pentas longiflora, cis-3,4-dihydroxy-3,4-dihydromollugin 2, and trans-3,4-dihydroxy-3,4-dihydromollugin 3 is described. The O-protected mollugins were dihydroxylated using OsO4 to achieve the corresponding cis-dihydroxy derivatives in excellent yield. The synthesis of trans-3,4-dihydroxy-3,4-dihydromollugin was achieved using Oxone in good yield. A mechanism for the formation of cis-3,4-dihydroxymollugin acetonide from the reaction of mollugin with Oxone is proposed.     

Photosolvolysis of 3,4-dichloroaniline in water : Evidence for an aryl cation intermediate

Irradiation of 3,4-dichloroaniline in water (λ > 290nm) gave 2-chloro-5-aminophenol with a conversion of 78±5%. The photolysis quantum yield at 313 nm of 0.052±0.003 was unaffected by cyanide (0.35 M) or pH changes between 4 and 12. A MO calculation indicated a large excited singlet state shift in electron density to the carbon undergoing substitution. The reaction is suggested to proceed through an aryl cation intermediate produced by heterolytic cleavage of the meta carbon-chlorine bond. Reaction from the triplet state is not considered likely since neither oxygen nor sorbic alcohol affected the quantum yield.     

3,4-Thienylene-ethynylene Oligomers

Several well-defined 3,4-thienylene-ethynylene oligomers with different chain lengths have been synthesized and characterized. X-Ray crystallographic analyses proved their unique, totally helical conformations.     

Photochemical studies on 3,4-epoxy-3,4-dihydro-2H-1-benzopyrans

Photochemical behaviour of 3,4-epoxy-3,4-dihydro-2H-1-benzopyrans, intermediates in the synthesis of pterocarpans, has been studied in various solvents. While ring contraction leading to 2,3-dihydrobenzofurans through a photodecarbonylation process was observed in cyclohexane, photoisomerisation leading to 3-chromanones was observed in acetone. This study has also been extended to antijuvenile hormone precocene(I) oxide.