Reactions of Thioketones with a Fluorinated ThioneS-Imide

Abstract

N-(1-Adamantyl)hexafluorothioacetone S-imide (1) reacts readily with aromatic thioketones 4a−e to afford 1,4,2-dithiazolidines 5a−e as products of [3 + 2] dipolar cycloadditions. Unexpectedly, cycloadducts 5d and 5e, obtained from thioxanthione (4d) and 4,4′-(dimethoxy)thiobenzophenone (4e), respectively, are found to decompose at room temperature and could not be isolated as pure compounds. Unlike aromatic thiones, adamantanethione (4f) did not react with 1 at ambient temperature. However, reaction did occur upon heating in a sealed tube, and the new 1,4,2-dithiazolidine 9, bearing two adamantyl moieties, was isolated as the major product. The structure of 9 has been determined by X-ray diffraction analysis. The connectivity of the heterocyclic ring in this product indicates that the mechanism of its formation must proceed by a different route involving another in situ generated sulfur-centered 1,3-dipole. Retrocycloaddition of the primary adamantanethione cycloadduct 13 liberates hexafluorothioacetone, which is subsequently captured by S-imide 1 to give tetrakis(trifluoromethyl)-1,4,2-dithiazolidine 8 as a crystalline product. The structure of 8 has also been confirmed by X-ray diffraction analysis.