Synthesis of tetrahydrobenzo[b]pyran under catalysis of NH4Al(SO4)2·12H2O (Alum)

A simple and efficient one-pot synthesis of tetrahydrobenzo[b]pyrans from the three-component reaction between dimedone, aldehydes, and active methylene compounds using NH4Al(SO4)2·12H2O (Alum) as a catalyst at 80 °C is described. The catalyst exhibits remarkable reactivity and is reusable.