A novel coupling reaction of 3-substituted 4-alkoxy and 4-aminocyclobutene-1,2-diones induced by TiCl4–Zn

The coupling of 3-substituted 4-alkoxy or 4-aminocyclobutene-1,2-diones induced by TiCl4–Zn was studied. It is interesting to find that the double bonds involved in the coupling reaction and the unsymmetrical coupling compounds were obtained as major or sole products. A possible mechanism mediated by titanium coordination intermediates is proposed.