A Convenient Synthesis of 1,2-Dithietes and 1,2-Dithioxo Compounds Stabilized by Buttressing and Resonance Effects, Respectively, by Sulfuration of Alkynes with Elemental Sulfur

Sulfuration of a series of alkynes by elemental sulfur was investigated. Alkynes carrying highly bulky substituents, 2,2,5,5-tetramethyl-3-hexyne (6a), 1,2-di-(1-adamantyl)ethyne (6b), 3,3-dimethyl-1-phenyl-1-butyne (6c), and 1-(1-adamantyl)-2-phenylethyne (6d), reacted with sulfur to give the corresponding stable 1,2-dithietes 7a—d in 46—65% yields. Less hindered alkynes reacted with sulfur to afford 1,4-dithiins and thiophenes as the final products which were derived from the initial products, 1,2-dithietes, via their tautomerization to the corresponding 1,2-dithioxo compounds, while extremely congested alkynes failed to react with sulfur even under forcing conditions. On the other hand, ynamines, a typical electron-rich alkyne, 1-diethylamino-2-phenylthioethyne (6o), 1-diethylamino-2-phenylselenoethyne (6p), and tetraethylethynediamine (6q) were sulfurated under milder conditions to afford resonance-stabilized 1,2-dithioxo compounds 19o—q as the principal products. Mechanism of the formation of 1,2-dithietes, 1,2-dithioxo compounds, and other products is discussed.