Abstract A number of 2-substituted 4, 5-dihydroxy-6-(substituted aminomethyl) pyrimidines (VIII) were prepared from the corresponding 2-substituted 4, 5-dihydroxypyrimidines (VII) by a new pyrimidine Mannich reaction. The structure of VIII was proved by an independent synthesis. Further study of this reaction led to the synthesis of a new class of compounds: the pyrimido [4, 5-e] dihydro-1, 3-oxazines (VI).