Convenient method for the ortho-formylation of phenols

Phenolic derivatives are formylated selectively ortho to the hydroxy group by paraformaldehyde with magnesium dichloride triethylamine as base. With a lkyl-substituted phenols excellent yields of the corresponding salicylaldeh yde derivatives were obtained. Similar results were obtained with chloro-su bstituted phenols and with 3-and 4-methoxyphenol while 2-methoxyphenol was unreactive. A good yield of methyl 3-formyl-4-hydroxybenzoate was obtained by this method as well, but generally phenols with electron-attracting grou ps reacted sluggishly; the long reaction times required caused the formatio n of by-products. particularly MOM-derivatives of the phenols.