THIOLENE

Catalytic reduction of thiophenes over cobalt catalysts leads to thiolane derivatives, or hydrocarbons. " Noncatalytic reductions of thiophenes by sodium or lithium in liquid ammonia leads, via the isomeric dihydrothiophenes, to complete destructions of the ring system, ultimately giving butenethiols and olefins. " Exhaustive chlorination of thiophene in the presence of iodine yields 2,2,3,4,5,5,-hexachloro-3-thiolene, Pyrolysis of thiophene at 850°C gives a... 

Aeeording to the IR speetra (neat), nitriles 63a,b exist as 3-thiolene-2-ones 64a,b. For = Ph, R = FI, in CDCI3 solution only the keto tautomer... 

Thus the reaction of the three geometrical isomers of 2,4-hexadiene with thiirane oxide afforded the three related 3-thiolene 5-oxides 154 depicted in equation 62104... 

Treatment of 3-thiolenes with BuLi provides the 2-anion 323, which may act as a butadiene 1-anion equivalent (i.e. 324)306. Treatment of 323 with alkyl halide gives the 2-alkylated product (325) in high yield306,307 (see equation 118). Acylation of 323 leads to the products 327 in which the acylated anions formed in situ under the basic conditions have undergone further acylation306. 

When 3-thiolene dioxide is treated with hydrogen peroxide, the corresponding epoxide is obtained313. The 3,4-trans-diols can be obtained by hydrolysis under acidic conditions (equation 120). 

Recently the non-catalytic reduction of thiophene and its homologs was thoroughly investigated (5), (6). The preparation of both 2- and 3-thiolenes (dihydrothiophenes) was studied and reported to occur in accordance with the following scheme ... 

Fluorination of tetrachlorothiophene with potassium tetrafluorocobaltate(III) gave 3,4-dichlorotetrafluoro-3-thiolene (156). Similar fluorination of thiophene yielded the 3-thiolene (157) and the thiolan (158) <71JCS(C)346, 72T43). It has been suggested that the fluorination proceeds by initial oxidation of thiophene to the cation-radical by the metal ion, and subsequent quenching of this by atomic fluorine (Scheme 30). 

Methyl-3-thiolen-2-one can be converted to 2-dimethylamino-5-methylthiophene in 20% yield by heating with HMPT (74T875). The suggested mechanism is shown in Scheme 148. 

Total rate constant to yield 3-thiolene-2-one (20%) and 4-thiolene-2-one (80%). 

Dihydroxy-5-methylthiophene can also exist in four tautomeric forms. The NMR spectrum in CDCI3 shows a doublet atS = 1.55 (CH3), a double quartet at 4.10 (H-5), a broad signal at 6.1 (OH), and a doublet at 6.32 (H-4). No other peaks were observed, and together with the IR and UV data (Table 77) the true structure of 2,3-dihydroxy-5-methylthiophene is 3-hydroxy-5methyl-3-thiolene-2-one 229. 

There are relatively few reports involving the Michael addition of cyanomethylphosphonate anions to unsaturated compounds. The reaction provides a methodology for the elaboration of new reagents but more frequently is used for the preparation of phosphonylated heterocycles. Under basic conditions, diethyl cyanomethylphosphonate adds to benzalacetophenone and 2-bcnzylidcne-3-methyl-4-nitro-3-thiolene-l,l-dioxide to give the addition products in modest yields.- - - " ... 

Nikolaenko, T.Y., Trukhin, E.V., Tebbi, J., and Berestovitskaya, V.M., Reaction of phosphorylated CH acids with 2-bcnz.ylidcne-3-inethyl-4-nilro-3-thiolene 1,1-dioxide, Zh. Obshch. Khim., 66, 1043, 1996 Russ. J. Gen. Chem. (Engl. Transl.), 66, 1018, 1996. 

KCoF4,63,64 with potassium hydroxide65,66 (Scheme 3). Tetrafluorothiophene (11) has also been prepared by a route involving a final dechlorination step using zinc (Eq. 15)67 and 2,5-difluorothiophene (13) by the unusual defluorination of 2,2,5,5-tetrafluoro-3-thiolene (12) over sodium fluoride.68 Perfluorobenzofuran (15) can be prepared by reaction of benzofuran (14) with CsCoF4, followed by defluorination with nickel.69... 

These compounds are much more difficult to handle and much less accessible than phenols. Neither 2-hydroxythiophene nor its 4-thiolen-2-one tautomer are detectable, the compound existing as the conjugated enone isomer, 3-thiolen-2-one, which can be obtained directly by oxidation of thiophene. ... 

The Structures and Reactions of Hydroxy-, Mercapto-, and Aminothiophens. - 3-Thiolen-2-one reacts as dienophile with... 

In the latter case, some (118) was also formed. The reaction of 3-thiolen-2-one with 1,3-cyclopentadiene proceeded rapidly at room temperature in the presence of boron trifluoride etherate, to give (119). An exception was the reaction with 1-methoxy-3-C(trimethyls ilyl)oxy]butadiene, which only led to silyl transfer, giving 2-(trimethylsiloxy)thiophen and 4-methoxy-but-3-en-2-one.6 The reaction between the ambient anion of the 5-methyl-2-hydroxy-thiophen system with carbon disulphide and methyl iodide gave (121) in 36% yield, in addition to the expected product (120). Tfie structure of the latter compound was proven by X-ray crystallography, and a reaction path for its formation was suggested. The... 

Furyl)-3-thiolen-2-one has been prepared. The easily available compound (22) has been converted into acids, amides, and a hydrazide. Electrophilic substitution in (22) occurred exclusively in the 5-position. The hydrazide was converted into 3-amino-4-ethoxythiophen via the acid. Evidence has been presented that these compounds exist as hydroxy- and/or amino-tautomers. Some 5-phenyl-3-hydroxy-thiophens have been prepared and their fungicidal and insecticidal activities evaluated. The cyclization of some 2-allylthiophen-3-thiols and 3-allylthiophen-2-thiols has been investigated. The thio-Claisen rearrangement of cyclopent-2-enyl 2-thienyl sulphide leads to (85) and (86). ... 

Thiophenes Containing Two Fluorinated Substituents 2,5-Difluorothio-phene was obtained from 2,2,5,5-tetrafluoro-3-thiolen 151. Compound 151 is a major product in the fluorination of thiophene over potassium tetrafluorocobaltate. ... 

Burdon, J. Parsons, 1. W. Highly fluorinated heterocycles. Part XIV. The conversion of 2,2,5,5-tetrafluoro-3-thiolen into 2,5-difluorothiophen an apparent example of the thermal elimination of molecular fluorine. J. Fluorine Chem. 1979, 13, 159-162. 

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