Synthesis of 2,5-Diiodopyrazine by Deprotonative Dimetalation of Pyrazine
Abstract
The deproto-metalation reactions of pyrimidine and pyrazine were regioselectively carried out using lithium tri(2,2,6,6-tetramethylpiperidino)cadmate in tetrahydrofuran at room temperature. This result was demonstrated by subsequent trapping with iodine to afford 4-iodopyrimidine and iodopyrazine in 71 and 63% yields, respectively. The same reaction performed on pyri-dazine afforded a mixture of the 3- and 4-iodo derivatives (55 and 41% yields, respectively). From pyrazine, the access to the 2,5-diiodo derivative (40% on a 25 mmol scale) proved possible using a larger amount of base (1 equiv instead of 1/3).
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