A facile and efficient synthesis of tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives using phosphate fertilizers MAP, DAP, and TSP as heterogeneous catalysts

A simple and efficient one-pot synthesis of tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives was described. These reactions were realized through a three-component condensation of aromatic aldehyde, malononitrile, and 5,5-dimethyl-1,3-cyclohexanedione or 4-hydroxy-6-methylpyran-2-one using phosphate fertilizers monoammonium phosphate, NH4(H2PO4)2, (MAP), diammonium phosphate, (NH4)2(HPO4), (DAP), and triple superphosphate, Ca(H2PO4)2.H2O, (TSP) as heterogeneous catalysts. Under optimal reaction conditions, these fertilizers show an excellent catalytic activity. Indeed, the tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives were obtained with good yields in short reaction times. Also, these fertilizers can be reused at least four times without significant loss of their catalytic activity. Therefore, their application can be contributing to the development of green chemistry.