Vinylthiophene

Dehydration to 2-vinylthiophene is better achieved from 2-(2-thienyl) ethanol with powdered potassium hydroxide in the presence of copper than from 1-(2-thienyl) ethanol. a-Chloro-2-thienylpro-pane undergoes a Wurtz reaction with active iron to give 3,4-di-(2-thienyl) hexane in low yield, which has also been obtained through coupling with n-butyllithium. ... 

Vinyl- and 3-vinylthiophene (73b and 77) are less reactive than the corresponding furans and show a notable preference for extra-annular addition due to the higher reactivity of the diene system, including the side-chain double bond. 2-Vinylthiophene is less reactive than 3-vinylthiophene. Whereas 2-vinylthiophene (73b) reacted with maleic anhydride and 1,4-benzoquinone to give cycloadducts in reasonable yield, 3-vinylthiophene (77) gave a higher yield of the cycloadduct [76, 77] (Scheme 2.31). 

Vinylpyridines react with a variety of ADC compounds. The initial Diels-Alder adducts can be isolated, although in many cases the major product contains two molecules of the ADC compound.186,187 Similarly, 2-vinylthiophenes react to give both 1 1 and 1 2 adducts,188 189 and 3-vinylindoles to give 1 1 adducts.190 ... 

Fig. 6-4 Dependence of the instantaneous copolymer composition F on the initial comonomer feed composition/i and the percent conversion for styrene (MO-2-vinylthiophene (M2) with r = 0.35 and r2 — 3.10. After Walling [1957] (by permission of Wiley, New York) from plot in Mayo and Walhng [1950] (by permission of American Chemical Society, Washington, DC).

One can show the drift of copolymer composition with conversion for various comonomer feed compositions by a three-dimensional plot such as that in Fig. 6-4 for the radical copolymerization of styrene (M, )-2-vinylthiophene (M2). This is an ideal copolymerization with r — 0.35 and r-L — 3.10. The greater reactivity of the 2-vinylthiophene results in its being incorporated preferentially into the first-formed copolymer. As the reaction proceeds, the feed and therefore the copolymer become progressivley enriched in styrene. This is shown by Fig. 6-5, which describes the distribution of copolymer compositions at 100% conversion for several different initial feeds. 

Finally, in this section of syntheses from thiophenes, a catalytic one-step meftod for the preparation of thieno[3,2-2>]thiophene (2) should be mentioned. Reaction of 2-ethylthiophene with SOj over CrjOj/AljOj at 450° afforded a 13% yield of thienothiophene 2, together with thiophene, 2-methylthiophene, 2-vinylthiophene, and 2-aceto-thienone [Eq. (45)]. Under these conditions formation of the isomeric thieno[2,3-6]thiophene (1) was not observed. 

The orientation of the CH=CH2 in 2-vinylfuran and 2-vinylthiophene is of the X,C-cis type (81RCR336), as expected from conjugative interactions which should largely prevail over dipole composition in these compounds. It is also worthy to note that in the radical anion of trans-1,2-di(2-thienyl)ethylene (71G10), the preferred conformation is the one with both the thienyl rings in the S,C-cis orientation (155). The azomethines of five-membered rings retain the X,N-cis conformation (156), like the... 

Bromotoluquinone, 35, 27 5-Bromo-2-vinylthiophene, 38, 89 Buchner funnel, cooling jacket for,... 

By analogy, 2-vinylthiophene reacts with tetrabromocyclopropene by [4 + 2] cycloaddition subsequent loss of HBr with concominant opening of the cyclopropane ring leads to the benzofbjthiophene derivative (310) in 32% yield (90TL4581). 

Several cycloaddition reactions of vinylthiophene and vinylbenzo[6]thiophene are known. 2-Vinylthiophene easily adds 4-phenyI-l,2,4-triazoline-3,5-dione to give (308) (74JA5591). 2-Vinyl-thiophenes also undergo stereospecific cycloaddition with singlet oxygen to produce the corresponding endoperoxides (Scheme 87) (75TL4471). 

The cyclic cooligomerization of 2-vinylthiophene with butadiene, catalyzed by nickel complexes, has given (312) and (313) in a 1 2 ratio (78IZV1469). 

Successive hydrolysis and dehydrogenation of the adduct of 2-vinylthiophene with maleic anhydride gives benzo[6]thiophene-4,5-dicarboxylic anhydride.366,367... 

Vinylthiophene and maleic anhydride afford a Diels-Alder adduct which is believed to have the structure 135.366,367 Hydrolysis of 135 and subsequent dehydrogenation of the product with sulfur gives benzo[6]thiophene-4,5-dicarboxylic anhydride,367 whereas dehydrogenation of 135 with sulfur, followed by hydrolysis and decarboxylation, affords benzo[6]thiophene.360... 

The reaction of 2-vinylthiophene 59 with DMAD in benzene at reflux afforded four compounds 60-63. (85T2435). Compound 60 was the result of a Diels-Alder cycloaddition followed by aromatization. The adducts 61 and 62 are obtained by an ene reaction. The structure of compound 63 was unique for cycloadditions of vinyl heterocycles. 

The reaction between the less reactive dienophile MP and 2-vinylthiophene 59 in CH2C12 was conducted at 100°C under pressure and four compounds, 64,65,66, and 67, could be isolated and characterized spectroscopically (85T2435). The adduct 67 is the result of a second addition of MP to the normal cycloadduct, followed by Diels-Alder elimination of ethylene in a way similar to that reported for -substituted 2-vinylpyrroles (Section II,A,3) (80JOC4515). It is useful to point out the structure of adducts 61, 62, and 65 because the ene reaction of thiophene compounds is not a common one (75TL4471). 

The results of this reaction changed when the conditions were slightly different. Other authors have reported that with MP in refluxing benzene for 2 days, the polymerization of 2-vinylthiophene 59 took place quite rapidly and no adducts could be isolated (89JHC397). However, when a neat 1 3 mixture of 59 and MP was heated in a sealed tube at 110° for 4 days, compound 69 was isolated in 70% yield. One of the striking contrasts of this reaction, in comparison with the addition of MP to l-methyl-2-vinylpyrrole 20a, is the different regioselectivity of the reaction between the disymmetric dienophile MP with the nonisolated intermediates. In this latter case the indole 27 was isolated. 

Diels-Alder reaction of 2-vinylthiophene with tetrabromocyclopropene gave functionalized benzothiophene by selective cleavage of the initial cycloadduct (Section II,C,1) (90TL4581). 

Vinylthiophene 59 underwent thermal dimerization, as did 2-vinylfu-ran (Section II,D,1), to give compound 219a (69MI1). In a similar way, the... 

Figure 7. Variation in the thiophene ratio (TR upper diagram) and Ternary plot showing the variation in the relative abundances of 2,3-dimethylthiophene, n-non-l-ene and 1,2-dimethylbenzene (lower diagram) with artificial maturation temperature for a suite of kerogen residues obtained from hydrous pyrolysis (72 hrs) of Kimmeridge kerogen (Dorset, U.K.). NB. Integrated peak areas for 2,3-dimethylthiophene also include 2-vinylthiophene.

If the mixture is too cold, the quaternization reaction will be delayed. On the other hand, if no cooling is provided, the reaction mixture may boil over spontaneously because of the exothermic nature of the reaction. Heat cracks the quaternary compound to 2-vinylthiophene which, if not removed by distillation, may undergo thermal polymerization. 

Chloro-2-vinylthiophene and 5-bromo-2-vinylthiophene have been prepared in 47% and 35% yields, respectively, by essentially the same procedure. 

Vinylthiophene has been prepared by the dehydration of a-(2-thienyl)ethanol,3-6 by the condensation of vinyl chloride with 2-thienylmagnesium bromide in the presence of cobaltous chloride,6 and by the dehydrochlorination of cc-(2-thienyl) ethyl chloride.7... 

Chlorovinyl methyl ketone, 32,29 5-Chloro-2-vinylthiophene, 38, 89 3,4-j co-A5-Cholesten-3,4-dioic acid, 35, 38... 

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