PREPARATION OF POLYFUNCTIONAL ARYL AND ALKENYL ZINC HALIDES FROM FUNCTIONALIZED UNSATURATED ORGANOLITHIUMS AND THEIR REACTIVITY IN CROSS-COUPLING AND CONJUGATED ADDITION-REACTIONS

Functionalized aryl and alkenyl iodides undergo an iodine-lithium exch ange at -90 to -80 degrees C providing polyfunctional organolithiums w hich are stable for a short time at these low temperatures and can be transmetalated to organozinc derivatives by the addition of zinc bromi de. The resulting unsaturated organozinc halides can then be warmed up and are perfectly stable at 25 degrees C. They react directly with to syl cyanide. In the presence of CuCN . 2LiCl, they add in a Michael-fa shion to alkylidenemalonates. In the presence of catalytic amounts of Pd(dba)(2) and TPP or TFP, they undergo readily a cross-coupling at 25 degrees C with aryl and alkenyl iodides. The Pd-catalyzed coupling of arylzinc bromides with aryl triflates could also be achieved by using dppf as a ligand and 60 degrees C as reaction temperature. Copyright (C) 1996 Elsevier Science Ltd