Some unusual reactions of disodium 2-oxo-1,3-dithiole-4,5-dithiolates with biselectrophiles

Reaction of disodium 2-oxo-1,3-dithiole-4,5-dithiolate (3) with dichloro-maleic anhydride (4), mucobromic acid (7) and its pseudoester 9 leads to the formation of the 1,3-dithiolo[4,5-b]-1,4-dithiins 6, 8 and 10. 3 condenses with cis-3,5-dibromo-cyclopentene (15) to yield the tricyclic compounds 16 and 17. 3 is silylated by trimethylsilyltriflate (19) to give the unstable bis(trimethylsilyl)-thioether 20 which reacts with aldehydes and ketones to furnish the 1,3-dithiolo[4,5-d]-1,3-dithiole-2-ones 22a-c.