An efficient process for the synthesis of trans-2,3-disubstituted-2,3-dihydro-4H-1-benzopyran-4-ones (chroman-4-ones)

The piperidine catalyzed Knoevenagel condensation of 2'-aryl/alkyl-2-hydrox yacetophenones 7 and aryl/alkylaldehydes 8 in refluxing isopropyl alcohol w ith azeotropic removal of water affords, in high yield, equilibrium mixture s of E- and Z-chalcones 9 and cis- and trans-chroman-4-ones 10 which are ef fectively isomerized in situ to the trans-2,3-diaryl/alkylchroman-4-ones, f ollowing the addition of 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) to the co oled reaction mixture and may be isolated in high purities (91-99%) by simp le filtration, with good to excellent yields (70-95%). (C) 2000 Elsevier Sc ience Ltd. All rights reserved.