Synthesis of 5-aryl-3-hydroxy-4H-pyran-4-ones

The palladium-catalyzed coupling reaction of 3-benzyloxy-5-bromo-2-methyl-4H-pyran-4-one (2b) with phenylboronic acid afforded efficiently 3-benzyloxy-2-methyl-5-phenyl-4H-pyran-4-one (3b-1), and the benzyloxy group of the resultant product was cleaved by hydrolysis with conc. hydrochloric acid in acetic acid to give 5-phenyl-3-hydroxy-2-methyl-4H-pyran-4-one (4b-1) in high yield. This method was applicable as a general method for synthesizing 5-aryl-3-hydroxy-4H-pyran-4-ones (4) from the 5-bromo-4H-pyran-4-ones (1)