α‐Thiotetronic Acids, II. Reactions of γ‐Alkylidene‐α‐Thiotetronic Acids

The α‐thiotetronic acid 1 reacts with amines predominantly with ring opening to give polyfunctionalized ketones ( 2 ) which readily cyclize to α‐tetramic acid amides ( 4a, b ). The reaction of α‐thiotetronate 6 with nucleophiles is more complex, leading to either an open‐chain derivative ( 8 ) or formation of an α‐thiotetronic acid amide ( 3b ) or an α‐tetramate ( 4f ). Treatment of 6 with sodium sulfide in air furnishes the salt of the 1,2‐dithiole 10. The dibrominated α‐thiotetronate 13a reacts with N and S nucleophiles predominantly by substitution, leading finally to the bisthiolactones 14 or the thieno‐1,2‐dithioles 17 .