The iron-catalyzed oxidative C−C homocoupling of diarylamines affords 2,2′-bis(arylamino)-1,1′-biaryls which represent crucial synthetic building blocks for an access to a range of seven-membered heterocyclic ring systems. Reaction with paraformaldehyde, diphenyl carbonate, and diphenyl sulfite as efficient 1,1-dielectrophiles led to dibenzo[d,f][1,3]diazepines, dibenzo[d,f][1,3]diazepinones, and dibenzo[c,e][1,2,7]thiadiazepine 6-oxides. The synthetic procedures enable short and practical routes to these 1,3-diazepine derivatives under mild reaction conditions and with a high tolerance of various functional groups.