Two-Carbon Ring Expansion of 1‑Indanones via Insertion of Ethylene into Carbon–Carbon Bonds

A rhodium-catalyzed
direct insertion of ethylene into a relatively
unstrained carbon–carbon bond in 1-indanones is reported, which
provides a two-carbon ring expansion strategy for preparing seven-membered
cyclic ketones. As many 1-indanones are commercially available and
ethylene is inexpensive, this strategy simplifies synthesis of benzocycloheptenones
that are valuable synthetic intermediates for bioactive compounds
but challenging to prepare otherwise. In addition, the reaction is
byproduct-free, redox neutral, and tolerant of a wide range of functional
groups, which may have implications on unconventional strategic bond
disconnections for preparing complex cyclic molecules.