Synthesis of six‐ and seven‐membered heterocycles by reaction of 1‐(2‐chloroethylthio)‐1‐alkynes and 1‐(3‐chloropropylthio)‐1‐alkynes with alkali metal sulfide, selenide and telluride

Reaction of RCCSCH 2 CH 2 Cl ( 1 , R = alkyl) compounds with dilithium disulfide (Li 2 S 2 ) in ethanol gives 3‐alkyl‐5,6‐dihydro‐1,4‐dithiins ( 2 , n = 2, X = S). With the alkali mono‐sulfide, M 2 S, dehydrochlorination to (vinylthio)alkynes RCCSCHCH 2 ( 3 ) predominates. Interaction between 1 , n = 2, and M 2 Se or M 2 Te (M = Li or Na) in liquid ammonia gives rise to dehydrochlorination as well as to attack on chlorine with intermediate formation of alkynethiolates RCCS − ( 4 ); if this reaction is carried out in ammonia‐free ethanol, the desired 5,6‐dihydro‐1,4‐thiaselenins and ‐thiatellurins ( 2 , n = 2, X = Se or Te) are, in some cases, obtained. The chloro sulfides RCCS(CH 2 ) 3 Cl ( 1 , R = alkyl or phenyl) with alkali metal sulfide, selenide and telluride yield respectively 3‐alkyl‐ or 3‐aryl‐6,7‐dihydro‐5 H ‐1,4‐dithiepins, the corresponding 6,7‐dihydro‐5 H ‐1,4‐thiaselenepins and 6,7‐dihydro‐5 H ‐thiatellurepins ( 2 , n = 3). When R in the starting compounds 2 is a Me 3 Si group, the unsubstituted compounds 2 ( n = 3, R = H) are formed.