Microwave assisted effective procedure for the synthesis of 1,8-dioxooctahydroxanthenes through one-pot condensation of aldehydes and dimedone using Phosphonitrilic Chloride as catalyst and tetra butyl ammonium bromide as phase transfer catalyst was described. Aromatic aldehydes having electron withdrawing or electron donating groups reacted with dimedone to give corresponding 1,8-dioxooctahydroxanthenes derivatives in moderate to good yields.