2-Substituted thiazolidines (IIIa-g) were prepared by the reaction of 2-alkylthiothiazolines (II) and active methylene compounds. The tetra-substituted double bonds of IIIa-g were resistant to catalytic hydrogenation. N-Halogenation of IIIb was effected by t-butylhypochlorite or bromine in methanol-chloroform. BF₃-etherate treatment of IIIb in acetic anhydride gave three products, VI, VII and VIII. This new method of furoxane formation was also applicable to the conversion of ethyl nitroacetate to VI. The mechanisms of the formations of VI and VII are proposed briefly in Chart 4.