Unusual friedel‐crafts reactions. 3. Synthesis of 2,4‐Diethoxychromans and their conversion into benzopyrylium perchlorates

Abstract By a coordinated reaction of phenols (I) and malonaldehyde‐bis‐(diethylacetal) (II) at ambient temperature, under unusual Friedel‐Crafts conditions, a class of new compounds, 2,4‐diethoxychromans (IV) has been synthesized. Subsequent treatment of IV in acetic acid with 70% perchloric acid produces 1‐benzopyrylium perchlorates (V).