Reductive dimerization of 2- and 6-iodopurines:: Side reaction in pd-catalyzed cross-coupling of iodopurines

In the presence of a Pd catalyst and a base, 6- and 2-iodopurine derivatives undergo reductive C-C dimerization with the formation of the corresponding 6,6'- or 2,2'-dimers. The best results of the dimerization were obtained in the presence of i- Pr2NEt as a base in DMF. Phosphine-free catalysts as well as catalysts containing phosphines can be used. In the presence of catalytic systems containing PPh3 the dimerization does not proceed. This dimerization may become an important side reaction in the Stille or the Suzuki-Miyaura reactions of iodopurines.