Selective ortho formylation of phenols

Gassman and Amick introduced two methods, both similar to 2,4-rearrangement to effect ortho formylation of phenols. Although products were obtained in only moderate (20-45%) yields, the reactions are attractive in effecting exclusive ortho substitution (Eq 

Entry Substrate with X % yield of 5 %yield of 6 from 5 Overall %yield of 6 from 1 

1 -7eq of substrate was reacted with 1eq of reagent (7) for 15 min at -70°C followed by the addition of Et N. This was followed by a water wash, organic b 

Another ortho formylation method that is useful since it is also applicable to phenols containing bulky substituents, involves three stages and furnish products in yields as high as 65%, even with di-ferf-butyl-phenols (Eq 1.40).  

Reaction of phenoxy-magnesium halides with orthoformates is an older method for regioselective ortho formylation and gives moderate yields (30-55%) with simple alkyl phenols, however yields are very low when bulky groups, halo, nitro or carboxy substituents are present (Eq 1.40). Contrary to this the formylation of free phenol with aluminum chloride-triethylorthoformate yields the para-isomer (Eq 1.40).  

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