Practical synthesis of thiirene 1‐oxides that possess two bulky alkyl substituents

Acetylenes that possess two bulky alkyl substituents reacted with sulfur dichloride to furnish the corresponding 2,3‐dialkyl‐2,3‐dichlorothiiranes (5) nearly quantitatively. The alkaline hydrolysis of 5 afforded 2,3‐dialkylthiirene 1‐oxides (10) in high yields. These two reactions could be successively carried out in one flask, and 2,3‐di‐tert‐butyl‐, 2,3‐di‐(1‐adamantyl)‐, and 2‐(1‐adamantyl)‐3‐tert‐butylthiirene 1‐oxides (10a–c) were obtained in 70, 80, and 90% yields, respectively, based on the starting acetylenes, thus providing the most convenient synthesis of thiirene 1‐oxides. Disulfur dichloride also reacted with acetylenes to give 5 in good yields with the elimination of one sulfur atom. Although the alkaline hydrolysis of 5 provided 10 exclusively, acid hydrolysis gave a mixture of α‐oxothioketone 9 and thiirene 1‐oxide 10 in modest yields. All thiirene 1‐oxides 10a–c isomerized to produce α‐oxothioketones 9 in high yields when heated in boiling toluene. Reactions of a bis‐acetylene (18) with disulfur dichloride and with sulfur dichloride gave a dihydropentathiepin (19) in high yields.