1-Aryl-1,2-diazabuta-1,3-dienes react with dimethyl malonate
to give hydrazonic intermediates that in turn are converted into
pyrrol-2-ones, 1-arylpyrazoles and 2-(3-oxopyrazol-4-yl)malonates.
The latter compounds represent an useful entry to 4-(2-oxopyrrol-3-yl)pyrazol-3-ones,
by means of the addition of another molecule of 1,2-diazabuta-1,3-diene
and subsequent cyclization of the adducts.
1,2-diazabuta-1,3-dienes - Michael additions - cyclizations - pyrroles - pyrazoles