Straightforward Xanthate-Mediated Synthesis of Functional γ-Thiolactones and Their Application to Polymer Synthesis and Modification

Abstract

Thiolactones allow catalyst-free polymer synthesis and modification under stoichiometric conditions at mild temperatures, without the need for tedious and costly purification steps. However, there is a need for simple and general methods for the preparation of functional thiolactones. We have developed a modular platform for γ-thiolactone synthesis based on free-radical xanthate addition to alkenes. Because of the ready availability of a great variety of functional vinyl, allyl, and maleimido derivatives, numerous substituents (exemplified here through alkyl, perfluoroalkyl, diethyl phosphonate, and N-substituted succinimidyl groups) could be efficiently attached to the γ-position of the thiolactone ring. A second substituent may be added in the α-position by proper selection of the xanthate leaving group. In all cases the target thiolactone was obtained in good yield from the xanthate:alkene monoadduct by consecutive Chugaev elimination and cyclization. The potential of these new substituted thiolactone building blocks for polymer chemistry was demonstrated via an amine–thiol–ene conjugation strategy which resulted in successful end-functionalization of amino-terminated polymers and a thiol–acrylate step-growth polymerization to prepare functional poly(ester amide)s. This versatile method for making functional thiolactones should find broad applications as a means to prepare new materials with original properties.