Synthesis of dihydrocoumarins catalyzed by acidic ion-exchange resin

Three dihydrocoumarins and one benzodipyran have been prepared via reactions of phloroglucinol with acrylic acids or substituted ones catalyzed by strongly acidic ion-exchange resin, of which the 5-hydroxy-3, 4, 6, 7-tetrahydrobenzo[1,2-b;5,4-b']dipyran-2,8-dione and 3,4-dihydro-5,7-dihydroxy-3-methylcoumarin are the firstly reported compounds. It was found that the substituted acrylic acids were less reactive than the acrylic acids, and the yields of 2a rised from 20% to 66% when the mixed solvent tulene-THF was used in place of single solvent toluene.