Von Pechmann coumarin synthesis

An acidic resin can be used in place of sulfuric acid for the von Pechmann" " coumarin synthesis. For condensalions such as Ihal of resorcinol with ethyl ticeto-acetate, the two resins indicated appear to he equally salisl actory (/eu-Karb is a British polystyrenesulfonic acid). Use of a resin slmplllled puriflcalion of the eroduot. 

Owing to exceptional sensitivity of the tricyclic phenol (A) to acidic reagents, direct condensation with 2-carbethoxycyclopentane-l,3-dione (i) under von Pechmann coumarin synthesis conditions proved impossible. However, the bromide (ii) readily underwent condensation to give the desired coumarin ring D when zinc carbonate was used both as catalyst and acid scavenger. 

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