5‐(1‐Hydroxyethylidene)‐1,3‐dimethylpyrimidine‐2,4,6(1 H ,3 H ,5 H )‐trione and four amino derivatives

In the structures of 5‐(1‐hydroxyethylidene)‐1,3‐dimethylpyrimidine‐2,4,6(1 H ,3 H ,5 H )‐trione, C 8 H 10 N 2 O 4 , (I), 1,3‐dimethyl‐5‐[1‐(propylamino)ethylidene]pyrimidine‐2,4,6(1 H ,3 H ,5 H )‐trione, C 11 H 17 N 3 O 3 , (II), and 5‐[1‐(2,2‐dimethoxyethylamino)ethylidene]‐1,3‐dimethylpyrimidine‐2,4,6(1 H ,3 H ,5 H )‐trione, C 12 H 19 N 3 O 5 , (III), there are no direction‐specific intermolecular interactions. The molecules in 5‐[1‐(benzylamino)ethylidene]‐1,3‐dimethylpyrimidine‐2,4,6(1 H ,3 H ,5 H )‐trione, C 15 H 17 N 3 O 3 , (IV), are linked into chains of edge‐fused rings by a combination of one C—H·O hydrogen bond and one C—H·π(arene) hydrogen bond, while the molecules in 5‐(1‐hydrazinoethylidene)‐1,3‐dimethylpyrimidine‐2,4,6(1 H ,3 H ,5 H )‐trione, C 8 H 12 N 4 O 3 , (V), are linked into a continuous framework structure by three distinct N—H·O hydrogen bonds, each involving a different O‐atom acceptor. Each of compounds (I)–(V) contains an intramolecular hydrogen bond, of the O—H·O type in (I) and of the N—H·O type in (II)–(V).