Transformation of 1,2-Dithiole-3-thiones Into 1,6,6aλ4-Trithiapentalenes via Reaction with Bromoethanones

We report the reactions of derivatives of 5-amino-3-thioxo-3H-1,2-dithiole-4-carboxylic acid 1 with bromoethanones and acylation agents. Two different routes were used to obtain the products, 3-(acylmethylidene)-3H-1,2-dithioles 4. These compounds were synthesized by acylation of compounds 1 on the amino group, followed by the reaction with bromoethanones and excess of triethylamine. Another method was based on the inverted order of the mentioned reaction steps and in absence of a base. The treatment of 4 with thionyl chloride gave new unsaturated fused lactones 13 whereas thionation led to desired 1,6,6aλ4-trithiapentalenes 5. The structures of products and the reaction mechanisms are discussed.