Uncommon reaction in 4-formyl phenols - substitution of the formyl group

4-formyl phenols with electron donating groups in ortho-position react with active alkyl halides in three directions: Williamson reaction up to 48%, aromatic substitution of the formyl group up to 36%, and addition to the ortho-position with dearomatization of the ring up to 10%. The ratio of the products depends on the substituents in the benzene ring and the used alkali and additives.