Ring fused 1,2,5-thiadiazoles from oximes and trithiazyl trichloride

Abstract

Trithiazyl chloride 1 converts the oximes of simple cyclic ketones into fused 1,2,5-thiadiazoles and bis-1,2,5-thiadiazoles in mild one-pot reactions. Cyclopentanone oxime gives the bisthiadiazole 3 (20%) in which all four methylene groups have been functionalised. Indan-1-one oxime 4 gives the thiadiazole 5 (63%), and tetralone oximes 6 and 8 give the bisthiadiazole 7 in low yields (20%) in complex reactions. Benzosuberone oxime 11 however gives only the monothiadiazole 12 (30%) which is not converted further with more trimer 1. These reactions probably occur by mechanisms analogous to those proposed earlier for the conversion of alkenes, alkynes, active methylene compounds and enamines into 1,2,5-thiadiazoles. Bisthiadiazole 3, a reactive analogue of fluorene, condenses with p-anisaldehyde to give 13 and is oxidised by PCC to the fluorenone analogue 15 in low yield; 15 is formed directly from cyclopentane-1,3-dione with trimer 1. Ketone 15 condenses with malononitrile and Hunig's base to give the dicyanomethylene derivative 17 (94%) which forms a black metallic 1 ∶ 1 complex with TTF at room temperature.