Reactivity of Vinyl Epoxides/Oxetanes/Cyclopropanes toward Arynes: Access to Functionalized Phenanthrenes

The reactivity of
vinyl epoxides/oxetanes/cyclopropanes toward arynes has been demonstrated
under mild conditions to give the corresponding phenanthrenes in moderate
to good yields. This transition-metal-free cascade process involves
a series of Diels–Alder reaction, ring-opening aromatization,
and ene reaction. Various functionalized phenanthrenes could be synthesized
utilizing the versatile hydroxy group. Interestingly, vinyl epoxides/oxiranes
experience preferentially the Diels–Alder reaction toward arynes
over nucleophilic attack of epoxides/oxiranes.