An Unusual Heterocyclic Transformation in Liquid Ammonia

By the action of liquid ammonia, the cyclpadducts of isothiocyanates with 3, 4-dimethyl-5-(2-hydroxy) ethylthiazolium ylides (Ia-b) are converted into spiro [3, 3a-dimethylperhydrofuro [2, 3-d] thiazole-2, 4'-(5'-iminoimidazolidine)] derivatives (IIa-b), while the reactions of liquid ammonia with N-benzyl analogues (Ic-e) afford 3-aryl-6, 8-dimethyl-2, 9-dithia-4, 6, 8-triazatricyclo [3, 3, 0, 11, 5] oct-3-enes (IIIa-c) involving an unusual base-catalyzed cleavage reaction of the fused spiro thiazolidine ring. A possible mechanism of the novel transformation reaction is suggested.