Thiophene 1,1-dioxides, reactivity

Cyclopropene also adds to less reactive, acyclic, dienes218), though it is worth noting that the reaction with cyclohexadiene only proceeds in 10% yield 219). Addition of a range of alkylcyclopropenes to thiophene dioxides leads to cycloheptatrienes, presumably by cheletropic elimination of sulphur dioxide from the intermediate adduct 220) ... 

The most successful polymerizations carried out by using a Diels-Alder step-growth reaction are those which generate a highly reactive A-B monomer in situ by the reaction of a bismaleimide with cyclopenta-dienone (12), 2-pyrone (6, 13), or thiophene dioxide (5) derivatives. The intermediate 1 1 adduct loses carbon monoxide, carbon dioxide, or sulfur dioxide, respectively, all to generate the same type of reactive AB monomer, which is converted rapidly to polymer. High molecular weight polymers are obtained (Reaction 4). 

Most of the synthetic approaches towards benzoannelated [2.2]paracyclo-phanes use the Diels-Alder reaction to build up the annelated rings [18,22,29]. [2.2]Paracyclophane-l-ene (32) and [2.2]paracyclophane-1,9-diene (42) can be considered as the simplest dienophiles for this purpose. Since the first syntheses of these compounds in 1958 by Cram et al. [32], various attempts have been made to get them to react with dienes in terms of Diels-Alder reactions. However, [2 + 4] cycloadditions were never observed [33], and could not be facilitated either by the application of high pressure, or the presence of Lewis acid catalysts Diels-Alder adducts were not even obtained with dienes such as tetrachloro-thiophene dioxide, known for its high reactivity in [2 + 4] cycloadditions with an inverse electron demand. All the more surprising was the observation that monoene 32 reacts smoothly with dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate at room temperature leading to a dihydropyridazine-annelated paracyclophane 39 in high yield [34a]. As reported for other tetrazine Diels-Alder reactions... 

With hapten 134, a close analog of the transition state, Hilvert etal developed the Diels-Alderase antibody 1E9 in which elimination of the product is programmed to avoid product inhibition. In their study, the cycloaddition of reactive thiophene dioxide 130 and maleimide 131 affords the unstable adduct 132 that spontaneously eliminates SO2 followed by air oxidation to yield a stable phthalimide 133 (Scheme 23). The structure of the final product 13 3 is significantly different from that of the Diels-Alder adduct 132, and product... 

A seven-step process (13JOC12330) shown below has led to the highly reactive diene and dienophile thiophene dioxide. Interestingly, the dioxo compound, unlike the sufoxide which dimerizes readily at 0°C, survives in solution for many hours at 100°C,thus allowing it to function as a diene or dienophile. In addition, new routes (not shown below) to 3,4-difluoro- and tetrafluorothiophenes was developed, and the previously unknown 2,3,4-tri-fluorothiophene was prepared. 

CNIX)/2 Wavefunctions of thiophen have been used as a basis in a consideration of the concerted Diels-Alder addition to thiophen, thiophen dioxide, and furan Lert and Trindle were able to rationalize the observed order of reactivity with the aid of qualitative ideas from perturbation theory. 

The by far more common and preparatively valuable dioxirane oxidation of divalent sulfur substrates is that of sulfides, to produce either sulfoxides or sulfones . Since sulfoxides are considerably less reactive than sulfides, the reaction outcome may be conveniently controlled by the stoichiometry of the oxidant For example, in the low-temperature oxidation of thiophene by an excess of DMD, the corresponding 1,1-dioxide (sulfone) has been obtained, albeit in low yield (equation 20). This is the first preparatively useful method for isolating this elusive sulfone, which also accentuates the importance of the neutral and anhydrous conditions under which the oxidations with the isolated DMD may be conducted. 

Cycloadditions of thiophene 1-oxides are well known the 1-oxides seem much more reactive dienes than the 1,1-dioxides. Thus oxidation of 2,5-dimethylthiophene at 0°C in the presence of benzoquinone gives (510), whereas 2,5-dimethylthiophene 1,1-dioxide needs much more drastic conditions to react with benzoquinone. Oxidation of... 

Volume 2 begins with a thorough survey of sulfur radical cations, covering their synthesis, structure, stability, and reactivity, by Prof. Richard Glass. Prof. Naomichi Furukawa and Prof. Soichi Sato describe recent developments in the area of hypervalent organosulfur compounds, and the volume is completed by a discussion of the chemistry of thiophene 1,1 -dioxides by Prof. Juzo Nakayama and Prof. Yoshiaki Sugihara. 

However, there was a remarkable difference in their reactivity toward cyclopentadiene. While 2,5-bis(methylsul-fonyl)thiophene 1,1-dioxide still reacted as a dienophile (Equation 55), substrates in which only one EWG is attached to the ring react as dienes (Equation 56), ultimately forming indene derivatives by extrusion of SO2. 

Although 3,4-dichloro-l,2,5-thiadiazole-l,1-dioxide (76) is related structurally to 3,4-dichlorothiophene-1,1-dioxide their chemical properties are quite different. The thiophene compound is a reactive diene and readily dimerizes via an auto Diels-Alder reaction. Furthermore, its chlorine atoms are unreactive toward weak nucleophilic reagents like water and alcohol. The thiadiazole compound, on the other hand, shows no tendency to dimerize and is highly reactive toward water and alcohol. 

In the case of the suifones, all of the valence shell electrons of the sulfur atom are utilized in bond formation and, as such, none remains to contribute to the n system of the ring. Thus, the suifones would be expected to behave as reactive conjugated dienes. Indeed, it is to be expected that thiophene 1,1-dioxides should be more reactive than the corresponding thiophene 1-oxides, a prediction that is not borne out in practice since, for example, in Diels-Alder reactions the sulfoxides tend to be somewhat more reactive than the suifones (76ACS(B)353). 

The latter compound is similar to 60 (R = C02Et) in reactivity toward acenaphthylene, undergoing [4 + 2]-cycloaddition/cheleotropic elimination to the known sulhnylamine Et02C—N=S=0, which was sufficiently stable to be isolated but underwent facile cycloaddition with 2,3-dimethyl-1,3-butadiene to give the thiazine sulfoxide 65. Although 64 is a fairly reactive molecule, the reactivity in cycloaddition reactions is less than that of 60, which is in keeping with the known differences in reactivity of thiophene 1-oxide and thiophene 1,1-dioxide. 

CSI reacts with carboxylic acids to form nitriles via the initial adducts (75) which lose carbon dioxide to give the N-chlorosulfonylcarboxamides (76) which with DMF afford good yields of the nitriles (77) (Scheme 36). This provides a valuable procedure for the conversion of carboxylic acids into the nitriles. In addition, thiophene (78), as well as other reactive heterocycles, reacts with CSI to yield the N-chlorosulfonylcarboxamide (79) which on treatment with DMF affords the nitrile (80) (Scheme 37). 

Thiophene 1,1-dioxidcs bearing electron-withdrawing substituents undergo a cycloaddition reaction with benzocyclopropene in tetrahydrofuran followed by sulfur dioxide extrusion to give annulenes 3 in 5-35% yield. The unsubstituted thiophene 1,1-dioxide is, however, not sufficiently reactive and undergoes dimerization rather than cycloaddition. ... 

Here, the parallels with benzenoid counterparts continue, for these compounds have no special properties - their reactivities are those typical of benzenoid aldehydes, ketones, acids and esters. For example, in contrast to the easy decarboxylation of a-acids observed for pyrrole and furan, thiophene-2-acids do not easily lose carbon dioxide nevertheless, high-temperatme decarboxylations are of preparative value (see also 17.12.1.2). "... 

A novel extrusion of S02 is reported for the dithiine dioxides 104 to afford low yields of the thiophenes 105 and 106. The exact step at which the S02 loss occurs is not known but the proposed intermediates 107 and/or 108 have support from the formation of pyrrole derivatives when the reaction is carried out in the presence of n-butylamine103. Sunlight-induced extrusion of sulphur dioxide from the pyranone dioxide 109 is similar to the above and results in the formation of the reactive cyclopentadienone 110 which can be trapped by dienophiles or in their absence forms a trimer104. The platinum complex 111 is photochemically labile and decomposes into benzyne on irradiation105. 

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