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2.5- dihydrothiophene-1,1 -dioxides dienes from

Hogeveen and Heldeweg found a rare example of a Diels-Alder reaction with sulfur dioxide where the [4 + 2] adduct is reasonably stable. Addition of sulfur dioxide to diene 76 at low temperature yielded [4 -I- 2] adduct 77 as the kinetic product. At temperatures above 2(J C products resulting from the dihydrothiophene dioxide 78 were observed (Scheme 1-XVI). [Pg.21]

The methiodide of 2,5-dihydrothiophene (239) is transformed in high yield to Z)-l-(methylthio)buta-l,3-diene (240) on treatment with alkali (81AJC1017). The thermal cheletropic extrusion of sulfur dioxide from both cis and trans isomers of 2,5-dihy-drothiophene 1,1-dioxides is highly stereospecific. For example, c/5-2,5-dimethyl-2,5-dihydrothiophene 1,1-dioxide (241) yields ( , )-hexa-2,4-diene (242) and sulfur dioxide (75JA3666, 75JA3673). [Pg.86]

The thiophene ring system can be utilized as a synthetic scaffold for the preparation of nonthiophene materials as the sulfur moiety can be removed by reduction (desulfurization) or extrusion (loss of SO2). The extrusion of sulfur dioxide from 3-sulfolenes (2,5-dihydrothiophene 1,1-dioxides) give dienes (butadienes or o-quinodimethanes) that can be utilized to prepare six-membered rings by cycloaddition chemistry. For example, thermolysis of 3-sulfolene 120 provided tricyclic pyrazole 122 via an intramolecular cycloaddition of the o-quinodimethane 121 that results by extrusion of sulfur dioxide <00JOC5760>. Syntheses of 3-sulfolenes 123 and 124 <00S507> have recently been reported. [Pg.97]

Chemical shifts and coupling constants indicate that thiophene 1,1-dioxides possess reasonable diene character <1984ZNB915>. The H NMR spectrum in CDCI3 shows the a- and /3-protons at 6.64 and 6.38 ppm, respectively, which is about 0.7 ppm upfield from the corresponding resonances in thiophene. Similarly, the H-2 and H-3 protons in 4,5-dihydrothiophene resonate at 6.06 and 5.48 ppm while that of the corresponding dioxide are found at 6.66 and 6.81 ppm, respectively. [Pg.662]

Five membered ring sulfones (thiolene-1, 1-dioxides, sulfolenes or dihydrothiophene-1, 1-dioxides) can be obtained by peracid oxidation of tetrahydrothiophene. The extrusion of sulfure dioxide from dihydrothiophene-1,1 dioxides or sulfolenes like (178) has been much studied as it provides a synthetic route to dienes, e.g. butadiene (152) (Scheme 70). The reverse reaction provides a method of synthesis of sulfolene (178) from butadiene (152) and sulfur dioxide. Thiolene dioxides or sulfolenes can be generally prepared by addition of sulfur dioxide to conjugated dienes for example, 1,4-dimethylbutadiene (179) in the presence of sulfure dioxide, triethylamine and formic acid affords 2,5-dimethylsulfolene (180) (Scheme 71). [Pg.215]

The theimolysis of 2-substituted 2,5-dihydrothiophene 1,1-dioxides leads to ( ) conjugated dienes via cycloieversion followed by the concerted cheletropic extrusion of sulfur dioxide. The thermolysis of the a, -alkylated sulfone (96) gives the intennediate, which loses SO2 to give 1-dodecadien-l-yl acetate (98), a component of the sex pheromone of the red bollwoim moth. Tliis procediue has been extended to the thermolysis of a,3-dialkylated sulfones in order to obtain ( , )-1,4-disubstituted-1,3-dienes (equation 46). Similar processes have been used for the syntheses of alkaloids. The synthesis of an Elaeocarpus alkaloid, elaeokwine A (100), makes use of the retrodiene extrusion of sulfur dioxide to give the 1,3-diene intermediate (99) that is subsequently consumed by an intramolecular imino DA reaction (equation 47). o-Xylylene (102) has been generated by rDA expulsion of SO2 from benzo-fiised 3,6-dihy(ho-l,2-oxathiin 2-oxide (101). ... [Pg.567]

Dihydrothiophene 1,1-dioxides from 1,3-dienes s. 6, 615 2,5-dienc-2,5-dihydro-thiophene 1,1-dioxides from conjugated diallenes s. K. Kleveland and L. Skatteb0l, Acta Chem. Scand. B 29, 827 (1975) 2,7-dihydrothiepin 1,1-dioxide ring s. W. L. Mock and J. H. McCausland, J. Org. Chem. 41, 242 (1976)... [Pg.152]

The cheletropic elimination reactions are widely used for generation of relatively unstable dienes in situ for Diels-Alder reactions. For example, extrusion of nitrogen from diazene 146, and sulfur dioxide from 2,5-dihydrothiophene-l,1-dioxide 147... [Pg.96]

Cycloadditions Interestingly, sulfur dioxide participated as a dienophile in the [4+2] cycloaddition reaction with 1,3-dienes. In this manner, sulfur dioxide reacts similarly to the related selenium dioxide and the other sulfur dienophiles RN=S=0, RN=S=NR and R2C=S=0 (sulfines). However, the [4+2] cycloadducts derived from 1,3-dienes and sulfur dioxide are only obtained at low temperatures (—80 °C) in a kinetically controlled reaction and the cycloaddition reactions often require the presence of a Lewis acid (CF3COOH or BF3). Above —50 °C the Diels-Alder adducts undergo a cycloreversion and a cheletropic addition of the generated sulfur dioxide to the diene occurs with formation of the corresponding 2,5-dihydrothiophene-1,1-dioxides (sulfolenes). According to ab-initio computations, electrostatic solvent effects are predicted to be of importance in the control of the selec-tivities in this reaction . From linear dienes, the [4+1] cycloadducts are usually obtained. For example, from 1,3-butadiene and SO2 at -20 °C, the cyclic sulfone 25 is obtained in 95% yield. ... [Pg.507]


See other pages where 2.5- dihydrothiophene-1,1 -dioxides dienes from is mentioned: [Pg.743]    [Pg.743]    [Pg.479]    [Pg.153]    [Pg.715]    [Pg.851]    [Pg.851]    [Pg.126]    [Pg.2057]    [Pg.2056]    [Pg.551]    [Pg.703]   
See also in sourсe #XX -- [ Pg.404 ]




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2,5 -dihydrothiophene-1,1 -dioxides

Dienes 2,5-dihydrothiophene-1,1 -dioxides

Dienes dioxides

Dihydrothiophene

From 1,2 dienes

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