Phospho sulfonic acid as efficient heterogeneous Bronsted acidic catalyst for one-pot synthesis of 14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes

A simple, efficient procedure for the preparation of phospho sulfonic acid PO(OSO3H)(3) as a Bronsted acidic and recoverable heterogeneous catalyst is described, used for the one-pot synthesis of aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes. A cost-effective, simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a,j]xanthenes was developed via a onepot condensation from substituted benzaldehydes and beta-naphthol under solvent-free conditions. The one-pot condensation of substituted benzaldehydes and 5,5-dimethyl-1,3-cyclohexanedione (dimedone) under solvent-free conditions leads to 1,8-dioxo-octahydro-xanthenes. These protocols afford a number of advantages, such as: excellent yields, very short reaction times, easy procedure, simple methodology and ease of preparation and regeneration of the catalyst. (c) 2014 Institute of Chemistry, Slovak Academy of Sciences