Efficient cross-coupling, allowing a straightforward access to congested benzophenones, between aromatic aldehydes and potassium aryltrifluoroborates, is described in the presence of a rhodium/tri-tert-butylphosphane catalyst system and acetone as cosolvent. The use of the stable phosphonium salts of tri-tert-butylphosphane prevented the use of highly oxidizable tri-tert-butylphosphane and allowed
A direct cross-coupling reaction of aromatic aldehydes with potassiumtrifluoro(organo)borates afforded ketones in high yields and under mild conditions in the presence of a rhodium catalyst and acetone. This new reaction, involving a formal aldehyde C-H bond activation, is believed to proceed via a Heck-type mechanism followed by hydride transfer to acetone.