Preparation of polyfunctional aryl and alkenyl zinc halides from functionalized unsaturated organolithiums and their reactivity in cross-coupling and conjugated addition reactions

Abstract

Functionalized aryl and alkenyl iodides undergo an iodine-lithium exchange at −90 to −80 °C providing polyfunctional organolithiums which are stable for a short time at these low temperatures and can be transmetalated to organozinc derivatives by the addition of zinc bromide. The resulting unsaturated organozinc halides can then be warmed up and are perfectly stable at 25 °C. They react directly with tosyl cyanide. In the presence of CuCN·2LiCl, they add in a Michael-fashion to alkylidenemalonates. In the presence of catalytic amounts of Pd(dba) 2 and TPP or TFP, they undergo readily a cross-coupling at 25 °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 °C as reaction temperature.