Conversion of 2-Iodobiaryls into 2,2′-Diiodobiaryls via Oxidation-Iodination Sequences: A Versatile Route to Ladder-Type Heterofluorenes

Even though 2,2′-diiodo- and 2,2′-dibromobiaryls represent accomplished precursors for heterofluorenes and other extended π-conjugated systems, their preparation still remains nontrivial when structural diversity of the biaryl backbone is required. Herein, we report a convenient method for the preparation of various 2,2′-diiodobiaryls from 2-iodobiaryls via cyclic diaryliodonium intermediates. An iodinative ring-opening of the diaryliodonium salts, mediated by a copper/diamine catalyst system, is able to afford the corresponding 2,2′-diiodobiaryls under mild conditions. The versatility of this two-step approach is demonstrated by the preparation of hitherto unexplored tetraiodoteraryls and their conversion into ladder-type π-conjugated systems. Biaryl iodination: 2-Iodobiaryls can be readily converted to 2,2′-diiodobiaryls through an initial oxidation to form cyclic diaryliodonium salts, followed by a copper/diamine-catalyzed iodinative ring-opening under mild conditions. The versatility of this two-step protocol is demonstrated by the preparation of hitherto unexplored tetraiodoteraryls and their conversion into ladder-type π-conjugated systems.