Efficient Solvent Free Synthesis of 12-Aryl-8,9,10,12-tetrahydrobenzo[a]-xanthen-11-ones and 3H-Spiro[isobenzofuran-1,9'-xanthen]-3-one Derivatives Using Cobalt Hydrogensulfate as a Green, Heterogeneous and Reusable Catalyst

     Cobalt hydrogensulfate is an efficient catalyst for the condensation of β-naphthol, aromatic aldehydes and 5,5-dimethyl-1,3-cyclohexanedione at 120 °C to afford 9,9-dimethyl-12-phenyl-8,10,11,12-tetrahydro-9-H-benzo[a]xanthen-11-one derivatives in high yields. Also, polycondensation reactions of phenols with phthalic anhydride were carried out in the presence of cobalt hydrogensulphate under solvent-free conditions. Simple and convenient procedure, high conversion, reusability of catalyst, easy purification and short reaction time are the advantageous features of this method.