Sterically hindered benzophenones via rhodium-catalyzed oxidative arylation of aldehydes

A simple reaction pathway to access congested benzophenone frameworks starting from readily available aryl aldehydes and potassium aryltrifluoroborates is described. The reactions proceed under neutral conditions in presence of stable phosphonium salt of P[(t-Bu).sub.3] to form di-, tri-, and even tetra-ortho-substituted benzophenones.