Synthesis of Pyrazines and Pyrimidines

Question 1

synthesis symmetrical pyrazines

Answer 1

double condensation of 2-aminocarbonyls then oxidation to regain aromaticity

Question 2

formation of 2-aminocarbonyls

Answer 2

ketone with NBS gives a-bromoketone then NaN3 gives carbonyl azide then hydrogenation to aminocarbonyl
OR
ketone with NaNO2 and HCl gives carbonyl-NO then hydrogenation to aminocarbonyl

Question 3

synthesis of unsymmetrical pyrazines

Answer 3

diamine condensation with 1,2-dicarbonyl then oxidation to regain aromaticity

Question 4

synthesis of pyrimidines

Answer 4

1,3-dicarbonyl and NCN fragment
OR
use 1,3-dicarbonyl fragment and use Claisen reaction
OR
DMF-DMA or orthoformates used to carbonylate ketones