A Convenient Synthesis of 3-Hydroxy-4H-pyran-4-one Derivatives Having a Halo or Hydroxy Group at the 5-Position
摘要:
The reaction of 4,5-epoxy-4-halo-6-methoxy-2-methyl-tetrahydropyran-3-ones (4b and 5b) in acidic media was examined and the following results were found: The reaction of 4b or 5b with 1% sulfuric acid afforded a mixture of 3,5-dihydroxy-4H-pyran-4-one (1b) and 5-halo-3-hydroxy-4H-pyran-4-one (2b or 3b), but the use of concentrated acid formed the corresponding 5-halo-4H-pyran-4-one (2b or 3b) only. The reaction was applicable for a general method for synthesizing 3,5-disubstituted 4H-pyran-4-ones (1, 2, and 3).
An unprecedented deconstructive reorganization strategy for the denovosynthesis of hydroxylated benzofurans from kojic acid- or maltol-derived alkynes is reported. In this reaction, both the benzene and furan rings were simultaneously constructed, whereas the pyrone moiety of the kojic acid or maltol was deconstructed and then reorganized into the benzene ring as a six-carbon component. Through this
The palladium-catalyzed coupling reaction of 3-benzyl-oxy-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).