Cyclopenta-1,2,3-dithiazoles and related compounds

Treatment of 3-phenylinden-1 -one oxime 6 with disulfur dichloride gives the indenodithiazole 2 directly in 58%; in the presence of Hunig's base the yield rises to 90%. Indenone oxime 9 and indanone oxime 11 with disulfur dichloride both give the chlorinated indenodithiazole 10, in up to 80% with Hunig's base. Similarly, cyclopentanone oxime gives the deeply violet trichlorocyclopentadithiazole 13(ca. 25%) at 4 °C in tetrahydrofuran with Hunig's base or in dimethylformamide without added base. A mechanism (see Scheme 1) is proposed for this extensive transformation in which a simple saturated oxime is converted into a highly functionalised heteroaromatic compound by the formation of 7 new bonds; this mechanism is based on the activation to chlorodeprotonation of all the cyclopentane positions, in turn, by the dithiazole ring. Analogously, cycloheptanone oxime 17 gives the red pentachlorocycloheptadithiazole 21, by the formation of 10 new bonds, and now di-, tri-, and tetrachloro intermediates, 18–20, can also be isolated; tetrahydrobenzocycloheptenone oxime 22 gives the analogous dichloro 23 and trichloro 24 compounds, and the acyclic oxime 25 gives the monocyclic dithiazole 27, all in modest yield. The chlorine in compound 10 is displaced by morpholine and pyrrolidine, but similar displacements in the trichloro compound 13 are unsuccessful since its heterocyclic ring is destroyed by nucleophiles. The pentachloro compound 21 is more stable than 13 towards nucleophiles, but less stable towards m-chloroperbenzoic acid, and these observations are explained in terms of the dipolar structures 13a and 21a.