Eschenmoser's salts: from design to applications in organic synthesis.

For over half a century, Eschenmoser's salt and related analogues have been widely exploited in organic synthesis, enabling the aminomethylation and α-methylenation of a broad range of substrates. Owing to their tunable structure and counterions, these salts exhibit remarkable versatility in homologation, C-C bond forming reactions, C-H functionalization, and in the synthesis of heterocycles, natural products, and biologically active compounds. This review highlights the structural modifications, reactivity, and applications of Eschenmoser-type iminium salts, emphasizing their continuing impact and adaptability in modern synthetic methodology.