Dithians, 1,4-Diselenans, 1,4-Dithiepans, and 1,5-Dithiocans

4-Dithians, 1,4-Diselenans, 1,4-Dithiepans, and 1,5-Dithiocans.—Formation. The ratio of 2-methyl-1,4-dithian (172) to 1,4-dithiepan (173) obtained on photocatalysed cyclization of the unsaturated thiol (174) was sensitive to 

4- dithian (179) being isolated in either case. At - 65 °C the predominant photocatalysed cyclization product was 5-methyl-1,4-dithiepan (178). In an intermolecular example, 3-methyl-but-2-enethiol photo-dimerized to a mixture of cis- and t/ fln5-2,5-di-isopropyl-l,4-dithian in good yield. Divinyl sulphone reacted with sulphur dioxide in the presence of a mixture of formic acid and formaldehyde as catalyst to give 1,4-dithian- 

4- tetroxide, and 1,4-dithian derivatives were also formed in the reactions of 1,2-di-immonium salts with sodium ethanedithiolate, and in the pyrolysis of polyethylene and polypropylene sulphide. The formation of 1,4-dithians by photocycloaddition of thiocarbonyl compounds to olefins has been reviewed.  

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