m-CPBA/TFA: an efficient nonmetallic reagent for oxidative coupling of 1,2-diarylethylenes

A mild synthesis of a series of phenanthrenes with different substituents on the phenanthrene ring is described. The method involves intramolecular oxidative coupling of a variety of 1,2-diarylethylene derivatives in the presence of m-chloroperoxybenzoic acid (m-CPBA) in trifluoroacetic acid (TFA) to yield phenanthrenes in high yields. The present approach solves a key step for the synthesis of polycyclic structures related to an alkaloid tylophorine.

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