Dimethylthioformamide condenses with 3-methyl(ene) -1.2-dithiolium salts in acetic anhydride to give 3-(2-dimethylaminovinyl)-l,2-dithiolium (Vilsmeier) salts. These salts react with sodium hydrogen sulphide to give thiothiophthenes. and with sodium hydroxide to form 3-acylmethylene-3H-I .2-dithioles. l H N.m.r. data for these compounds are discussed. An improved procedure for the synthesis of 1.2-dithiolium salts is described.MUCH work has been carried out on the bonding 2 9 3 and structure 4-9 of thiothiophthenes since the spatial arrangement of the carbon and sulphur atoms of the dimethyl derivative (IIIe) was established lo by crystallographic studies. Little is known, however, of the t. The compounds represented by formula (111) have received various non-systematic names such as meribicyclo-3,5-epidithiopenta-2,4-dienthials 41 and thi~thiophthenes.~-j. '-lo, l5 The latter, being the most commonly used, is employed in this paper.
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