Preparation and pyrolysis of some Bi- and Tri-cyclic sulfones derived from photochemical [2 + 2] cycloaddition of 2,3-dihydrothiophene 1,1-dioxide (2-sulfolene)

Photochemical reaction of 2,3-dihydrothiophene 1,1-dioxide [2-sulfolene] with maleic anhydride gives the [2 + 2] cycloadduct 8 and simple reactions of the anhydride function provide access to a wide range of new bi- and tri-cyclic sulfones 9-13 and 15-24 containing the novel 2-thiabicyclo[3.2.0]heptane 2,2-dioxide ring system. On pyrolysis these undergo either cycloreversion with elimination of 2-sulfolene or in one case extrusion of ethene and SO2 to give the 1,3-diene. Oxidative bis-decarboxylation of the diacid from hydrolysis of 8 gives the new simple alkene sulfone 31. Pyrolysis of this results in loss of only SO2 to give cyclohexa-1,3-diene, but its epoxide 34 loses SO2 and ethene to afford furan, thus making 31 a synthetic equivalent of cyclobutadiene.