One-Pot Multistep Reactions Based on Thiolactones: Extending the Realm of Thiol−Ene Chemistry in Polymer Synthesis

Abstract

The in situ generation of thiols by nucleophilic ring-opening of a thiolactone with amines, followed by a UV-initiated radical thiol-ene reaction in a one-pot fashion, has been evaluated as an accelerated and versatile protocol for the synthesis of several types of polymeric architectures. After elaboration of a model amine-thiol-ene conjugation reaction, a number of routes based on readily available thiolactone-containing structures have been developed to successfully assemble functional, linear polymers and networks via a mild and facile radical photopolymerization process.

One-Pot Double Modification of Polymers Based on Thiolactone Chemistry

“…The combination of thiolactone aminolysis and the radical thiol-ene process, so-called radical amine-thiol-ene conjugation (Scheme 5, pathway a), was performed on a mixture of benzylamine, N-acetylhomocysteinethiolactone 2, and norbornene as low molecular weight model compounds in order to master the reaction conditions [48]. The solution was irradiated by an external UV light source, and 2,2-dimethoxy-2-phenyl acetophenone (DMPA) was selected as an efficient photoinitiator for thiol-ene conjugation [118].…”

“…Furthermore, thorough analysis of the reaction mixture obtained after the two-step reaction revealed the formation of side products originating from the reaction between benzylamine and radical fragments of DMPA. However, using optimal conditions (no photoinitiator) and after a straightforward chromatographic purification, the model reaction yielded the conjugation compound with an isolated yield of 80% [48].…”

“…Two different AB 0 monomers, susceptible to radical amine-thiol-ene conjugation, were synthesized and successfully used in a photopolymerization, yielding linear polymers with either a polythioether/polyurethane [48] or a polythioether/ polyamide backbone [48,55].…”

“…First, some functional groups (e.g., furan [119][120][121][122][123], double and triple bond) introduced via the amine are incompatible with this radical environment. Additionally, UV curing takes place upon decomposition of a photoinitiator (e.g., DMPA), but model studies revealed that some amines (e.g., benzylamine) react with the formed radical fragments, thus limiting the use of a photoinitiator [48].…”

“…Despite the fact that click reactions involving thiols [36][37][38][39][40][41][42][43] are valuable metal-free alternatives to the copperassisted azide-alkyne cycloaddition (CuAAC) reaction [44][45][46][47], thiol-related issues (smell, shelf life, and synthetic availability) prevent their widespread use. Hence, the reactivity of a γ-thiolactone (a five-membered cyclic thioester) as a latent thiol functionality has recently been investigated by us [48][49][50][51][52][53][54][55][56][57][58] and others [59][60][61][62][63][64][65][66]. Synthetic concepts based on thiolactone chemistry generally share a common feature: a thiol is released by nucleophilic ring opening (aminolysis) and subsequently reacts with a thiol 'scavenger' (Scheme 1).…”