Lewis acids Pechmann coumarin synthesis

The most important FBAs in the coumarin series are the 7-amino-3-phenylcoumarins which are prepared via the Pechmann coumarin synthesis. For example, m-aminophenol may be condensed with ethyl 3-hydroxy-2-phenylacrylate in the presence of a Lewis acid in nitrobenzene (Scheme 13). 

The Pechmann coumarin synthesis, also known as the Pechmann condensation or Pechmann reaction, is the Lewis or Bronsted acid-promoted condensation of phenols (1) and P-keto (or other 3-oxo aliphatic) esters (2) to produce coiunarins (2//-chromen-2-ones, 3). ... 

The long-established Pechmann synthesis of coumarins has been revisited. The reaction of phenols with ethyl acetoacetate (EAA) occurs in better yield at lower temperatures and milder conditions in ionic liquids which act as both solvent and Lewis acid catalyst <01TL9285> and in solvent free reactions catalysed by 4-TsOH <01CL110>. Microwave irradiation of aminophenols and EAA on a solid support of graphite and montmorillonite KIO rapidly gives good yields of 4-substituted 7-aminocoumarins <01TL2791>. 

Potdar, M. K., Mobile, S. S., Salunkhe, M. M. 2001. Coumarin synthesis via Pechmann condensation in Lewis acidic chloroaluminate ionic liquid. Tetrahedron Lett. 42 9285-9287. 

Via a Lewis acid such as AICI3 (Scheme 3) and in general (Scheme 4). The synthesis of coumarin with simple phenols under the Pechmann... 

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