Intramolecular Base-Free Catalytic Wittig Reaction: Synthesis of Benzoxepinones

A straightforward
two-step synthesis of benzoxepinones was developed
via base-free phosphane-catalyzed Wittig reaction. 3-Methyl-1-phenyl-2-phospholene
1-oxide was used as a precatalyst and trimethoxysilane as a reducing
agent. Additionally benzoic acid is employed as a catalyst to facilitate
the reduction of the phosphane oxide. Mechanistic investigation revealed
the formation of a coumarin as a side product, which was identified
by 2D NMR experiments. First results of metabolic activity tests on
the prepared benzoxepinones are reported.