The nonenolisable diketone was prepared by employing the
modified procedure reported earlier [11]. Acetylacetone (10 g,
10 mmol) was mixed with substituted aromatic aldehyde
(10 mmol) and piperidine (1–2 drops) in ethanol (50 ml), and the
reaction mixture was stirred thoroughly for a period of 3–6 h with
occasional cooling. Gradually a yellow precipitate separated in
small amounts. The reaction mixture was set aside to evaporate
to dryness and the residual solid was washed with an excess of
petroleum-ether to remove any unreacted reagents. Washing was
repeated two to three times and the compound was recrystallized
from ethanol to give a yellow solid Knoevenagel condensate. The
structure of the ligand is shown in Scheme 1.