Deprotonative Metalation of Chloro- and Bromopyridines Using Amido-Based Bimetallic Species and Regioselectivity-Computed CH Acidity Relationships

A series of chloro- and bromopyridines have been deprotometalated by using a range of 2,2,6,6-tetramethylpiperidino-based mixed lithiummetal combinations. Whereas lithiumzinc and lithiumcadmium bases afforded different mono- and diiodides after subsequent interception with iodine, complete regioselectivities were observed with the corresponding lithiumcopper combination, as demonstrated by subsequent trapping with benzoyl chlorides. The obtained selectivities have been discussed in light of the CH acidities of the substrates, determined both in the gas phase and as a solution in THF by using the DFT B3LYP method.