Simple and cost effective acid catalysts for efficient synthesis of 9-aryl-1,8-dioxooctahydroxanthene

CaCl2 (20 mol %) dispersion in DMSO or aq HBr (10 mol %) is developed as an efficient and cost effective acid catalyst for the simple one-pot synthesis of 9-aryl-1,8-dioxooctahydroxanthene derivatives. Reaction of aromatic aldehyde (1 equiv) and dimedone (2 equiv) in the presence of CaCl2 (20 mol %) in CHCl3 at room temperature gave the open chain analogue of 1,8-dioxooctahydroxanthene. Similarly, aq HBr (10 mol %) in water at reflux temperature gave a high yield of 9-aryl-1,8-dioxooctahydroxanthene derivatives. The use of inexpensive, eco-friendly and readily available catalysts, easy work-up, and isolation of the products makes these procedures a convenient method for the synthesis of either of the products.