Benzo 1,3-dihydrothiophene dioxide

Cheletropic elimination of sulfur dioxide from benzo(c)-l,3-dihydrothiophene dioxide (8) was used as a route to c-quinodimethanes [550]. 

The theimolysis of 2-substituted 2,5-dihydrothiophene 1,1-dioxides leads to ( ) conjugated dienes via cycloieversion followed by the concerted cheletropic extrusion of sulfur dioxide. The thermolysis of the a, -alkylated sulfone (96) gives the intennediate, which loses SO2 to give 1-dodecadien-l-yl acetate (98), a component of the sex pheromone of the red bollwoim moth. Tliis procediue has been extended to the thermolysis of a,3-dialkylated sulfones in order to obtain ( , )-1,4-disubstituted-1,3-dienes (equation 46). Similar processes have been used for the syntheses of alkaloids. The synthesis of an Elaeocarpus alkaloid, elaeokwine A (100), makes use of the retrodiene extrusion of sulfur dioxide to give the 1,3-diene intermediate (99) that is subsequently consumed by an intramolecular imino DA reaction (equation 47). o-Xylylene (102) has been generated by rDA expulsion of SO2 from benzo-fiised 3,6-dihy(ho-l,2-oxathiin 2-oxide (101). ... 

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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