2- and 6-Purinylmagnesium Halides in Dichloromethane: Scope and New Insights into the Solvent Influence on the C−Mg Bond

The generation of positionally stable purin-2- and 6-yl magnesium halides is complicated by the often very rapid isomerization to give the 8-yl Grignards. By conducting the reaction in dichloromethane (DCM), we demonstrated that the anion isomerization can be stopped and these stable purin-2- and 6-yl Grignards react directly with a broad scope of aldehydes in good yields. Furthermore, purine functionalization with ketones has been achieved for the first time in the presence of LaCl3 ⋅ 2LiCl. Density functional theory calculations offer a possible explanation of the special role played by solvent in this chemistry and show that in DCM the C−Mg bond has a less polar character, whereas in THF it is predominantly ionic and much more basic in nature.