Thiophene with maleic anhydride

What would be the result of reacting benzo[c]thiophene with maleic anhydride, then hot NaOH, then acid - the product has the formula C12H8O4 ... 

H. Kotsuki, F. Nishizawa, S. Kitagawa, M. Ochi, N. Yamasaki, K. Matsuoka, T. Tokoroyama, High pressure organic chemistry HI. Diels-Alder reactions of thiophene with maleic anhydride, BuU. Chem. Soc. Jpn. 52 (1979) 544—548. 

H. Kotsuki, S. Kitagawa, H. Nishizawa, T. Tokoroyama, Diels-Alder reaction of thiophene with maleic anhydride at very high pressure, J. Qrg. Chem. 43 (1978) 1471-1472. 

Endo adducts are usually favored by iateractions between the double bonds of the diene and the carbonyl groups of the dienophile. As was mentioned ia the section on alkylation, the reaction of pyrrole compounds and maleic anhydride results ia a substitution at the 2-position of the pyrrole ring (34,44). Thiophene [110-02-1] forms a cycloaddition adduct with maleic anhydride but only under severe pressures and around 100°C (45). Addition of electron-withdrawiag substituents about the double bond of maleic anhydride increases rates of cycloaddition. Both a-(carbomethoxy)maleic anhydride [69327-00-0] and a-(phenylsulfonyl) maleic anhydride [120789-76-6] react with 1,3-dienes, styrenes, and vinyl ethers much faster than tetracyanoethylene [670-54-2] (46). 

NH2)50s(2,3-T -L)], where L = furan, pyrrole, and thiophene. Although neither the furan nor thiophene complexes react with maleic anhydride over a period of 10 days, the pyrrole complex (15) reacts rapidly at room temperature and 101.3 kPa to form a mixture of endo (17) and exo (16) complexes. An a2omethine ylide intermediate was postulated as the key intermediate through which maleic anhydride added to the 2- and 5-positions of the coordinated pyrrole ring. 

Thiophene fails to undergo cycloaddition reactions with common dienophiles under normal conditions. However, when thiophene is heated under pressure with maleic anhydride, the exo adduct (136) is formed in moderate yield (78JOC1471). 

Benzo[Z)]furans and indoles do not take part in Diels-Alder reactions but 2-vinyl-benzo[Z)]furan and 2- and 3-vinylindoles give adducts involving the exocyclic double bond. In contrast, the benzo[c]-fused heterocycles function as highly reactive dienes in [4 + 2] cycloaddition reactions. Thus benzo[c]furan, isoindole (benzo[c]pyrrole) and benzo[c]thiophene all yield Diels-Alder adducts (137) with maleic anhydride. Adducts of this type are used to characterize these unstable molecules and in a similar way benzo[c]selenophene, which polymerizes on attempted isolation, was characterized by formation of an adduct with tetracyanoethylene (76JA867). 

Furukawa and coworkers reported preparation and isolation of thiophene 1-oxides 111-113. Diels-Alder reaction of 111 with maleic anhydride, benzoquinone, and cw-l,2-dibenzoylethylene gave the corresponding syn adducts exclusively [61] (Scheme 50). 

A novel route to reduced dibenzothiophenes bearing substituents in the 3,4-positions has been described involving treatment of 3-vinyl-benzo[6]thiophene (25) with maleic anhydride or tetracyanoethyl-ene to give 26 and 27, respectively, as shown in Scheme 3. 

Substituted benzo[ ]thiophene derivatives have been prepared in excellent yields by a tandem Pummer rearrange-ment/Diels-Alder reaction of the intermediate furan with maleic anhydride or A -phenylmaleimide (Equation 87) <1996JOC6166>. 

While the Diels-Alder reactions of thiophenes with various dienophiles are relatively rare, it is interesting to note that 2,5-dimethoxythiophene (297) prepared from 2,5-diiodothiophene does react with maleic anhydride to form the bis-adduct (299) (75JCS(P1)2483>. Sulfur extrusion from the primary cycloadduct delivers a new diene system (298) which then undergoes the second Diels-Alder reaction (Scheme 63). 

Turning now to activation of the thiophene molecule, it has been shown that 2,5-dimethoxythiophene reacts with maleic anhydride to give the bis-adduct (293) in 42% yield (75JCS(Pl)2483). Initial addition of maleic anhydride followed by the usual sulfur extrusion leads to a diene, which then adds another molecule of maleic anhydride (Scheme 81). 

Vinylbenzo[6]thiophene is reported to form a Diels-Alder adduct with 1,4-naphthoquinone (70AHC(ll)i77>. The 3-vinyl isomer is known to be a reactive diene its cycloaddition products with maleic anhydride, p-benzoquinone, benzyne, etc. have been described. 

Diels-Alder reactions of thiophene 1,1-dioxides are very common (B-67MI31401). With rare exceptions, the adduct loses a molecule of SO2 to form a diene which may add another molecule of the dienophile. The sequence with maleic anhydride is shown in Scheme 193. It has been claimed that in the reaction of thiophene dioxide with acetylenedicarboxylic ester the primary adduct could be isolated, but this could not be substantiated (75RTC85). 

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

In contrast to the adducts of many dienes with maleic anhydride, the above adducts are characteristically stable to heat some do not dissociate at temperatures as high as 300°. This property is apparently associated with the sulfone group, since reduction of the anthracene adduct (346) with lithium aluminum hydride affords the corresponding cyclic sulfide, which readily dissociates at 250° to give anthracene and benzo[6]thiophene.726... 

Furan is readily hydrogenated, hence it is a source of commercial tetrahydrofuran (THF). Reaction with hydrogen sulfide over alumina produces thiophene. A recent patent describes a catalyst based on cobalt and molybdenum oxides supported on alumina for this reaction (105). Furan undergoes the Diels-Alder reaction with strong dienophiles. Hydrogenation of the product resulting from reaction with maleic anhydride, followed by hydrolysis and neutralization gives a herbicide, Endothall. 

It is known that thiophene (34) is more aromatic than pyrrole and does not undergo IEDAR under conventional conditions. However, almost 25 years ago, it was reported that the reaction with maleic anhydride (35) at 1.2-2.0 GPa and a temperature of 100 °C produced the exo adduct 36 in 40% yield [37]. Recently, highly improved results have been attained under high-pressure and solvent-free conditions (Scheme 11) [38]. 

Scheme 11 IEDAR of thiophene (34) with maleic anhydride (35) under high-pressure/ solvent-free conditions [38]...

This ester cannot be dehydrogenated with palladium-charcoal, selenium, or chloranil 16 similar attempts to aromatize 4,5,6,7-tetrahydrobenzo[c]thiophene have failed.616 Diethyl 4,5,6,7-tetra-hydrobenzo[c]thiophene-l,3-dicarboxylate forms an adduct with maleic anhydride.6... 

Benzo[c]thiophene readily forms adducts with maleic anhydride (m.p. 153°-154°,5 6 148°-152°52), dimethyl acetylenedicarboxylate (see above),61 and A-phenylmaleimide (to give 62).52,61 In the last case the exo and endo isomers of the adduct may be separated by fractional crystallization.52 Benzo[c]thiophene reacts with acetyl nitrate by 1,3-addition in preference to substitution.6 It exhibits halochromy with concentrated sulfuric acid, trichloroacetic acid, and stannic chloride.62... 

---