I suggest you to use KOH or NaOH as base in place of piperidine. and also you should try aromatic aldehydes in place of aliphatic aldehydes and simply stir the mixture at room temperature.

Water has nothing to do with this reaction.

I tired with KOH and NaOH but the problem still there. I tried at different concentration of bases but after 3-4 days of stirring at Rt and even at heating both reactant still present in reaction mixture.

Have you further worked up?

Yes after 3-4 days i did the workup. Both reactant were present.

I suggest working with an azeotrope system filled with the reaction solvent which is ethanol to trap the water given off by the reaction.

Will toulene work?

It has around 26⁰C difference in temp. Between its azeotropic mixture

What is your aldehyde?

4 Formylpyrazole

You are performing the aldol condensation rather than Claisen. The reaction may be carried out under either acid or base catalysis. Acid-catalyzed reaction is perhaps not the best option for 4-formylpyrazole. With the base-catalyzed reaction of PhC(O)Me with benzaldehyde, NaOH as a catalyst is used as per the following procedure suggested by J. B. Ellern:

"A modification for use in undergraduate labs is given for preparation of benzalacetophenone (BZAP) from PhCHO (0.1 mol) and PhCOMe (0.1 mol) at ambient temperature NaOH pellets (0.5-1.0 g) are dissolved in 1-1.5 mL water, 20-5 mL MeOH is added, and the solution is cooled to 20-2°. Twelve mL PhCOMe and 10 mL PhCHO were added and swirled. After 15-20 min, the mixture abruptly breaks cleanly into 2 phases, the lower phase being oily and yellow and the upper phase being mobile and nearly colorless. BZAP is separated from the solution." (Ellern, James B.

J. Chem. Education (1979), 56(6), 418).

As your aldehyde might be less reactive than PhCHO, the molar percentage of NaOH should be at least as high or somewhat higher.

The reaction may be also carried out under the phase-transfer conditions in DCM-water using cetylpyridinium chloride or Aliquat as a catalyst. Good luck.

See also Biletch, Harry A.; Rajunas, Joseph V., Jr., US3361827:

"A mixture of MeOH 1.5, H2O 4, NaOH 1.3, benzaldehyde 1, and acetophenone 1 mole was kept at 15-27° 3-6 hrs., a seed crystal of chalcone added after 3 hrs., the liquid decanted after an addnl. hr., H2O added, the mixture heated to 60°, the pH adjusted to 6.5-7.0 with 3N HCl, the chalcone melted at 60°, and stirred and frozen at 40° to form beads. The beads were separated, washed with H2O, then a small amount of cold MeOH and oven-dried to give 90% yield of chalcone, m. 55-7°."

First of all, you do not need to apply heating to your synthesis. This reaction doesn't require heating keep temperature 10-25 degree Celsius using ice bath. Use catalyst KOH or NaOH check the reagents that you are you are using.

and one thing that you may not be aware of is that chalcone derivative always shows very close rf value to one of your reactants, it could be aldehyde. then you need to check if one of your reactants looks less concentrated in the tlc plate then. Now you can go for turn pH of the reaction mixture 7.0 precipitation will come automatically, if not then you need to add DI or distilled water into your reaction mixture itll leads to formation of precipitation. then just filter and take a tlc.