Formylation of Phenols with Electron-withdrawing Groups in Strong Acids. Synthesis of Substituted Salicylaldehydes

抄録

Salicylaldehydes with electron-withdrawing groups, i.e., 2-hydroxy-5-nitrobenzaldehyde (2a), methyl 3-formyl-4-hydroxybenzoate (2b), methyl 5-chloro-3-formyl-2-hydroxybenzoate (2c), 3, 5-dichloro-2-hydroxybenzaldehyde (2d), 5-cyano-2-hydroxybenzaldehyde (2e), and 5-fluoro-2-hydroxybenzaldehyde (2f), were synthesized by the formylation of the corresponding phenols (1a-f) with hexamethylenetetramine in 75% polyphosphoric acid, methanesulfonic acid, or trifluoroacetic acid. The yields of these reactions were better than those of the Duff reaction.