Ortho Formylation

A simple way of formylating phenols is using paraformaldehyde, combined with anhydrous magnesium chloride and triethylamine in refluxing THF.  The reaction gives selective ortho formylation and for some phenols, selectivity for only one of the ortho positions is achieved ( (Akselsen O W et al, Tet Lett, 2009, 50, 6339-6341)