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.