Synthesis of biaryls via benzidine rearrangement

Beside para,para-direction, the rearrangement always produces a small amount of ortho,para- pro xicX, probably via non-concerted, forbidden suprafacial [3,5]-pathway [88], For example, hydrazobenzene (501), beside benzidine (502), produces very small, but isolable, amount of ortho,para-proA xcX, diphenyline (516). 

In conclusion, the 4,4 -diaminobiaryls are efficiently obtained by the benzidine rearrangement of A/,A -diarylhydrazines, which are readily available from ortho- and weta-substituted anilines as starting materials. 

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