Rhodium-Catalyzed (4+1) Cycloaddition between Benzocyclobutenones and Styrene-Type Alkenes.

Herein, we describe a unique one-carbon ring-expansion strategy to access multi-substituted 2-indanones from benzocyclobutenones and styrene-type olefins. The use of a cationic "ligandless" rhodium catalyst was the key for both high reactivity and selectivity towards the (4+1) product. Broad functional group tolerance, a good substrate scope, and scalability have been demonstrated. Computation studies reveal that the origin of the (4+1) selectivity is due to a facile ß-H elimination pathway that reduces the overall barrier of the turnover-limiting C-C reductive elimination step.

Asymmetric Synthesis of 1-Tetralones Bearing A Remote Quaternary Stereocenter through Rh-Catalyzed C-C Activation of Cyclopentanones.

Herein, we describe the preparation of 1-tetralones bearing a remote quaternary stereocenter in a highly enantioselective manner. A sequence of Pd-catalyzed asymmetric 1,4-addition and Rh-catalyzed enantiospecific C-C/C-H activation delivers diverse 1-tetralones with a C4 quaternary stereocenter, which are prepared in good overall yields and high enantioselectivity.

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.