Rhodium-catalyzed tandem cyclization: formation of 1H-indenes and 1-alkylideneindans from arylboronate esters in aqueous media.

Arylboronate esters bearing a pendant Michael-type acceptor olefin or acetylene linkage undergo transmetalation with a rhodium-based catalytic complex to generate a functionalized organorhodium intermediate which can cyclize onto nonterminal acetylenes in good to excellent yields. The catalytic system involves the use of electron-rich, sterically bulky ligands as tri-tert-butylphosphonium tetrafluoroborate stabilizing the organorhodium intermediates and reduces the incidence of protodeboronation in aqueous media.