3- Methyl-2,5-dihydrothiophene 1,1-dioxide

Alkenes with a reduced electron density, for example 3-methyl-2, 5-dihydrothiophen 1,1-dioxide, react with NO BFS" to give... 

This category is represented in the facile reaction of o-phenylenediamine (408) with 4-benzoyl-5-phenyl-2,3-dihydro-2,3-thiophenedione (409) (in toluene at 20°C for 30 min) to afford 3-(a-benzoyl-p-mercaptostyryl)-2(l//)-qumoxalinone (410) in 98% yield " also in the complicated reaction of 3-methyl-2,2,4-trinitro-2,5-dihydrothiophene 1,1-dioxide (411) with 2 equiv of ethyl 4-aminobenzoate (412) (in acetonitrile but no further details) to give ethyl 2-(p-ethoxycarbonylphenyl)-3-(l-methyl-2-nitrovinyl)-6-quinoxalinecarboxylate (413) in 51% yield.Several... 

Another example of type iii-a is the trifluoromethylation of double bonds by electrolysis of trifluoroacetic acid in the presence of olefins. Methyl vinyl ketone, vinyl acetate, diethyl fumarate, diethyl maleate, Ai-ethylmaleimide, and 2,5-dihydrothiophene-l,1-dioxide were examined as olefins. The products were bis-trifluoromethylated additive dimers (66) (type iii-a) and monomers (67) (type... 

A [5 - 2 + 2 + 1] fragmentation followed by cyclization forming a new five-membered ring was observed by FVP studies of 2-propenyl-l,3-dithiolan 1,1-dioxide (79) (95H1967). The reaction mixture consists of four products thiophene (26%), 2,5-dihydrothiophene (80,34%), 4-methyl-2-propenyI-4//-l,3-dithiine (20%), and 2,6-dimethyl-2//,6//-l,5-dithiocine (20%). The last two compounds are formed by [4 + 2] or [4 + 4] dimerization of the intermediate 2-butenethial. Formation of 80 involves a 1,5-H shift of the as-butenethial, followed by cyclization. 

The solvent-dependence of cheletropic reactions has also been investigated [158aj. The thermolysis of 3-methyl-2,5-dihydrothiophene-l,1-dioxide appears to involve a concerted fission of the two (T-bonds. This is in accordance with the very small solvent effect on rate observed in six solvents of different polarity [158a]. 

Methoxycarbonyl-2,5-dihydrothiophen-l,l-dioxide (methyl 3-sulfolene-3-carhoxylate)... 

Dibromo-2,5-dimethylthiophene-l,l-dioxide (203) reacts with piperidine in benzene to form 3-bromo-2-methyl-4-piperidino-5-piperidinomethyl-c -4,5-dihydrothiophene-l, 1-dioxide (205)... 

Reaction of 3,4-dimethylthiophene-1,1-dioxide with benzylthiolate at room temperature gives 3-benzylthiomethyl-4-methyl-2,5-dihydrothiophene-l,1-dioxide (208) in 86% yield. Again an exomethylene tautomer is implicated. A similar reaction takes place with iec-amines. With the 2,5-dimethyl isomer (202a), reaction with benzylthiolate is analogous to that with aqueous piperidine. 

Reaction of the bromo compound (202b) with sodium ethoxide in ethanol leads to trans and cis (ratio 4 1) 2-ethoxymethyl-3-ethoxy-5-methyl-2,3-dihydrothiophene-1,1-dioxide. 

The reaction of 3,4-dimethyl-2,5-dihydrothiophen 1,1-dioxide, in which the double bond is blocked by the methyl groups, apparently proceeds ia an electrophilic substitution mechanism [92],... 

Syntheses of the parent [6]radialene (5) were published by three research groups in 1977/1978 4, 5, 6. Among the various gas-phase flash pyrolysis reactions reported, the triple HCl-elimination from l,3,5-tris(chloromethyl)mesitylene (109) is the most practicable one and yields the radialene in 35 -48% yield (Scheme 4.23) [5] other flash pyrolyses were carried out, typically at 900 °C, with cyclododeca-l,5,9-triyne, benzo[l,2 4,5]dicyclobutene derivatives and benzo[l,2-c 3,4-c 5,6-c"]tris(2,5-dihydrothiophene 1,1-dioxide). The sixfold dehydrobromination of hexa(bromomethyl)benzene (110) with methyl lithium at low temperature has been achieved more recently in this case, 5 has been trapped without isolation by cyclopropanation reactions yielding spiro compounds 111 in very low yield [88]. Radialene 5 is a diSicult-to-handle, extremely air-sensitive compound with properties [5] that resemble those described for the parent radialenes 2 and 3 see Sections 4.2.1 and 4.2.2. 

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