4,4'-BI(CYCLOBUTENE-1,2-DIONES) - BISQUARYLS

4,4'-Bi(cyclobutene-1,2-diones), novel compounds derived from squaric acid, here named bisquaryls, were prepared for the first time either by the palladium-catalyzed oxidative dimerization of (tri-n-butylstannyl)cyclobutene-1,2-diones (providing symmetrically substituted bisquaryls) or by a palladium-copper cocatalyzed cross-coupling of 3-substituted-4-(tri-n-butylstannyl)-3-cyclobutene-1,2-diones with 3-halo-4-substituted-3-cyclobutene-1,2-diones (providing a route to unsymmetrically substituted bisquaryls). The novel parent bisquaric acid is a very strong Bronsted acid that apparently fully ionizes on dissolution; only one pK(a) value (pK2 = -4.49) was observed.