The use of homogeneous and heterogeneous Lewis acids to catalyse the photoisomerizations of phenols

The reaction of methyl substituted phenols with CH 2 Cl 2 solutions of Al 2 Br 6 , leads to the formation of two types of complexes. In both of these the aluminum is bound to the oxygen atom of the phenol but they differ in that the OH proton can either remain on oxygen, oxonium complex, or migrate to one, usually the para, ring carbon, keto complex. The equilibrium position between the two types of complex depends on the position of the methyl …