Acetylenic thiolesters as a source of thioketenes

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Abstract
1‐Acetylthio‐1‐hexyne, magnified image , is cleaved by nucleophilic reagents. With primary and secondary amines, RR′NH (R = alkyl or aryl, R′  H or alkyl), N‐substituted acetamides CH3CONRR′ and N‐substituted thioamides C4H9CH2C(S)NRR′ are produced in good yields, the latter compounds presumably via the thioketene C4H9CHCS. In the case of ammonia, mainly acetamide and the polymer of the thioketene are obtained. Acethydrazide and 3,6‐dipentyl‐1,4 dihydro‐1,2,4,5‐tetrazine, I, have been isolated from the reaction mixture of acetylthiohexyne and hydrazine hydrate. Potassium amide, dissolved in liquid ammonia, converts acetylthiohexyne into hexynethiolate, C4H9CCSK (and acetamide); subsequent addition of ethyl bromide gives ethylthiohexyne, C4H9CCSC2H5, in excellent yield. If acetylthiohexyne is allowed to react with a mixture of ethanethiol and sodium ethanethiolate in dimethylformamide, the intermediate thioketene is trapped to produce the dithioester C4H9CH2C(S)SC2H5.