CLAISEN‐Condensations with Selected Dithioesters ‐ Synthesis of Special 3‐Methylthio‐acrylnitriles.A useful synthetic route to the mono‐ and diheteroaryl‐3‐methylthio‐acrylnitriles1and2is demonstrated by the thioanalogous CLAISEN‐condensation.In the presence of sodium hydride in tetrahydrofurane or under PTC‐conditions heteroaryl dithiocarboxylic esters3react with CH‐acidic compounds4or9to form 3‐mercapto‐acrylnitriles (e. g.5). Methylation leads to mono‐ and diheteroaryl‐3‐methylthioacrylnitriles1and10(type2). In the same manner tetrathioterephthalic ester6reacts with two equivalents of CH‐acidic compounds yielding8and11. By means of spectroscopic methods, especially1H‐ and13C‐n.m.r., the structures of