Abstract
The Vilsmeier-Haak reaction on 3-methylpyrazolone azosulphonamide derivatives (1,2) has been shown to lead to chlorination of the 5-oxopyrazolone system in addition to diformylation of the 3-methyl group to give the corresponding aminoacroleins (3,4), respectively. On treatment with some reagents 3, 4 give compounds 9–20 with different heterocyclic systems in the 3-position.