A rapid and simple method to access unnatural 2-substituted 5-thio oxazolines has been developed. This methodology is based on a Pummerer reaction followed by an intramolecular nucleophilic substitution, which changes the paradigm for the normal use of a base in Pummerer chemistry. We also provide a useful two-step method for the synthesis of the starting material and a mechanistic proposal based on experimental observations, which contests the previously proposed reaction pathway. The reaction proved to be general, and different substituents, such as alkyl, aryl, alkenyl and functionalized groups, can be used without a significant decrease in efficiency.

Reactions of Cu(ClO4)2⋅6H2O with 2,6‐bis(3,5‐dimethylpirazol‐1‐ylmethyl)pyridine (dmpz‐py) (1), 2,6‐bis(4‐iodo‐3,5‐dimethylpirazol‐1‐ylmethyl)pyridine (I‐dmpz‐py) (2) and 2,6‐bis(4‐nitro‐3,5‐dimethylpirazol‐1‐ylmethyl)pyridine (NO2‐dmpz‐py) (3) yield the corresponding metal complexes: [Cu(dmpz‐py)(H2O)(ClO4)]ClO4 (4), [Cu(I‐dmpz‐py)(H2O)](ClO4)2 (5) and [Cu(NO2‐dmpz‐py)(H2O)(ClO4)2] (6). The complexes were isolated in high yields as stable solids at room temperature and characterized by melting point, electrical conductivity, and infrared and ultraviolet/visible spectroscopy. In addition, the crystal structures of the new complexes were determined by single‐crystal X‐ray diffraction and showed square‐base pyramidal (4), distorted square‐planar (5) and octahedral (6) geometries. All three complexes were active in the ring opening polymerization of ϵ‐caprolactone under solvent‐free conditions, producing polycaprolactones of narrow polydispersity and high crystallinity. The results obtained show an important increase in polymerization speed compared with analogous azole‐derived copper (II) complexes.

A simple method to access unnatural 2‐substituted 5‐thio oxazolines (II) from sulfoxides (I) is described.