Ortho-Formylation of Phenols: the Casnati-Skattebøl Reaction in the Synthesis of Biologically Active Substances.

The Casnati-Skattebøl reaction is an effective method for achieving ortho-formylation of phenols to provide salicylaldehydes. The conversion involves the reaction of magnesium phenolates with formaldehyde followed by an oxidation of the intermediate hydroxymethyl group. This reaction has been used in the synthesis of numerous biologically active substances and natural products, which is the subject of this review.