Synthesis of new hydroxy-2-styrylchromones

Hydroxy-2-styrylchromones 5a-i were prepared by debenzylation of benzyloxy-2-styrylchromones 3a-i, which were synthesised by the Baker-Venkataraman method. The last step of this method, the cyclodehydration 5-aryl-3-hydroxy-1-(2-hydroxyaryl)-2,4-pentadien-1-ones 2a-i, was carried out with a catalytic amount of iodine, or p-toluenesulfonic acid, in DMSO. Benzyloxy-3-cinnamoyl-2-styrylchromones 4a-f were obtained as by-products in both procedures, but the latter procedure gave benzyloxy-2-styrylchromones 3a-i in better yields. The structures of all new compounds were established by extensive NMR studies. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).