Iron-catalyzed cascade addition/cyclization of 2-biphenyl isocyanides with toluenes: a highly efficient approach to 6-benzylated phenanthridines.

A highly efficient Fe-catalyzed cascade addition/cyclization of 2-biphenyl isocyanides with toluenes for the synthesis of 6-benzylated phenanthridines has been reported. Di-tert-butyl peroxide (DTBP) was employed as both a radical initiator and an oxidant. The procedure tolerates various functional groups, providing the corresponding products in moderate to good yields. The proposed mechanism involves the cascade addition of benzyl radicals to the isocyanides and the following radical aromatic cyclization.