Biocatalytic Regioselective C‐Formylation of Resorcinol Derivatives

ABSTRACT Although aromatic formylation reactions are highly valuable from a synthetic perspective, a biocatalytic version has not yet been reported. Here, the cofactor‐independent multimeric three‐component acyltransferase from Chromobacterium sphagni ( Cs ATase) was identified to enable the nonnatural promiscuous regioselective C‐formylation of polyphenolic substrates, especially resorcinol derivatives, and thus extending the reaction scope of acyltransferases. Formylation of 4‐ and 5‐substituted resorcinol derivatives gave access to regioselectively mono‐formylated products with up to 99% conversion and up to 74% isolated yield. Formylation of phloroglucinol led to the di‐formylated product with 99% conversion, outperforming chemical methods. Structural analysis of Cs ATase by X‐ray crystallography provided insights into its active site.