2,4- vs 3,4-disubsituted pyrrole synthesis switched by copper and nickel catalysts.

A novel and efficient copper or nickel catalyzed highly selective denitrogenative annulation of vinyl azides with aryl acetaldehydes has been developed. 2,4- and 3,4-diaryl substituted pyrroles, which are difficult to synthesize by the reported methods, can be highly regioselectively prepared by this protocol simply switched by the selection of the transition metal catalysts. Compared with the reported acidic or basic conditions for polysubstituted pyrrole synthesis, the present reaction conditions are mild, neutral, and very simple without any additives.