Synthesis of Pterocarpan-Type Heterocycles via Oxidative Cycloadditions of Phenols and Electron-Rich Arenes

Abstract

Oxidation of 4-alkoxyphenols or 4-methoxynaphthol with phenyl iodonium(bis)trifluoroacetate (PIFA) in the presence of electron rich 2H-chromenes or dihydronaphthalenes affords pterocarpans or 5-carbapterocarpans via a formal [3 + 2] cycloaddition process. Acid-catalyzed ionization of quinone dimethylmonoacetal in the presence of 7-methoxy-2H-chromene gave similar results, suggesting a phenoxonium ion intermediate in the oxidative process.

Keywords:

• Carbapterocarpan
• cycloaddition
• hypervalent iodine reagent
• oxidation
• phenol
• pterocarpan
• quinone monoacetal

ACKNOWLEDGMENTS

We gratefully acknowledge the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this work. Also acknowledged are Dr. Albert V. Fratini for his assistance in obtaining the x-ray crystal structure data and Mr. Justin Williams for obtaining high-resolution mass spectral data.