Pyrylium salt as a visible-light-induced photoredox catalyst for polymer and organic synthesis - Perspectives on catalyst design and performance

In recent years, there has been growing interest in photo-mediated processes. Herein, this review aims to give a summary concerning photoinduced processes in which pyrylium salts are involved. Synthetic methods leading to obtaining pyrylium salts are presented as well as properties of these compounds are described in detail. The second part of the review aims to summarize recent progress in the field of photoinitiators and photocatalysts. The use of pyrylium compounds as photoredox catalysts in organic reactions (cyclization, dimerization, cycloaddition, deprotection, rearrangement) is elucidated. Application of pyrylium salt derivatives in the role of initiators in photopolymerization processes (cationic photopolymerization, free-radical photopolymerization, photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) and ring-openingmetathesis polymerization ROMP) was also outlined.