Reaction of azoarenes with tributyltin hydride

Tributyltin hydride causes the reduction of azoarenes giving substituted hydrazyls in desired amounts and selectivity. Reactions involving the reduction of azoarenes with ortho substituents to the azo function, produce heterocyclic compounds of low selectivity. Whereas, reactions involving stannyl free radicals and azoarenes require the presence of a radical initiator such as alpha,alpha'-azobis(isobutyronitrile), so that reactions follow a radical chain mechanism.