1,2-Dichalcogenins: Simple Syntheses of 1,2-Diselenins, 1,2-Dithiins, and 2-Selenathiin

Ring opening of titanacyclopentadienes 1 with (SCN)2 or (SeCN)2 followed by bis(thiocyanate) or bis(selenocyanate) cyclization affords 1,2-dithiin (2 a) or 1,2-diselenin (2 b), respectively. Compound 1 gives 2 a directly on reaction with S2Cl2. Unsubstituted 1,2-diselenin is prepared by reaction of PhCH2SeNa with 1,4-bis(trimethylsilyl)-1,3-butadiyne followed by reductive cleavage of the benzyl group and oxidation. The unsubstituted 2-selenathiin is prepared in an analogous manner, but from a mixture of PhCH2SeNa and PhCH2SNa.