The Bergman cyclization has been the subject of renewed interest with
the discovery of naturally occurring enediyne-based antitumor agents t
hat cleave DNA by means of an aromatic diradical. These natural substr
ates have a means to trigger this cycloaromatization process. Control
of this reaction by substrate modification would allow aromatic diradi
cals to be generated selectively. in the studies presented here it is
disclosed that the Bergman cyclization of 1,2-bis(diphenyl phosphinoet
hynyl)benzene was accelerated by a factor of >30,000 by the addition o
f palladium(II) chloride or platinum(II) chloride and was inhibited by
the addition of mercury(II) chloride.