Selective monoacetalization of symmetrical aromatic dialdehydes has been achieved using pyridinium tosylate as a catalyst: Can. J. Chem., 51, 3756 (1973); Tetrahedron Lett., 39, 4179 (1998). Ketones have been immobilized by the addition of a catalytic amount of scandium triflate in the presence of trimethylorthoformate in toluene: Tetrahedron Lett., 41, 1691 (2000).