L-Proline Catalyzed Synthesis of Novel 5-{[2-(2-phenylpiperazin-1-yl)quinolin] methylene}-2,4-dione Derivatives

L-proline is found to be an efficient catalyst for the Knoevenagel condensation of 2-chloroquinoline-3- carboxaldehyde 1a-c with an active methylene compound i.e., 2,4-thazolidinedione 2 in IPA affording novel substituted olefins 3a-c. The latter products reacted with N-substituted-3-phenylpiperazine 4a-c in the presence of KF in DMF to afford the corresponding 5-{[2-(2-phenylpiperazin-1-yl)quinolin]methylene}-2,4-dione derivatives 6a-i. Alternatively, 6ai were also synthesized from another reaction sequence 1 → 5 → 6. The structures of the synthesized compounds have been established on the basis of spectral and analytical data. Keywords: 2-chloroquinoline-3-carboxaldehyde, 2, 4-thazolidinedione, L-proline, Knoevenagel condensation, N-substituted-3- phenylpiperazine.