Synthesis of Substituted Cyclohexenones from the Condensation of Acetone with 1,3-Diaryl-2-propen-1- one

Claisen-Schmidt condensation had been used to prepare a series of 1,3-Diaryl-2-propen-1-one (1-10), under strong basic condations. The prepared chalcones (1-10) were condensed with acetone to afford the corresponding cyclohexenones (11-20). The structures of the final products had been identified in the light of valid spectral methods (U.V.,I.R.) as well as the typical identification tests .In addition, to the theoretical calculations of heat of formation H.F. and Steric energy S.E. were used to support the suggested reaction mechanism.


Experimental 1-Instrumentation
a. Melting points were determined by Electrothermal 1A 9000 Digital series 1998 apparatus(uncorrected). b. Ultra-Violet spectra were obtained using Shimadzu UV-Vissible Spectophotometer UV-160. c. Infra-red spectra were recorded on Perkin-Elmer 590 B spectrophotometer. d. The theoretical calculations based on the data obtained from the minimized geometry were computed using semi-empirical AM 1 module in the CS ChemOffice molecular modeling package.

2-preparation of Chalcones (1-10) [1,3-Diaryl-2-propen-1-one]
General procedure (21) : A mixture of (2.2gm,0.055 mole) of sodium hydroxide pellets ,(20 ml) of water and (12.5 ml, 0.2 mole) of ethanol was stirred in a 100 ml round-bottomed flask provided with a mechanical stirrer and immersed in an ice-bath. A (0.043 mole) of freshly distilled of the desired acetophenone was poured on the stirred mixture followed by (0.043 mole) of freshly distilled benzaldehyde. With a vigorous stirring for (2-3)hrs the temperature of the mixture was kept at (20-25)C o , until the mixture become thick (stirring was no longer effective). The obtained mixture was then kept in an ice chest or a refrigerator overnight. The product was filtered under vacuum and washed with water until the filterates were neutral to Litmus, then washed with (20 ml) ice-cold ethanol. After drying the crude chalcone in air, it was recyrstallized from ethanol. The product should be handled with care since it cause a skin irritation. The names and some physical properties were illustrated in Table -1. The spectral and elemental data were shown on Table-2. The melting points ,infrared and ultraviolet data were in a good agreement with the reported values (22,23) .

Condensation of Chalcones with (24) acetone Preparation of Substituted Cyclohexenones(11-20)
In a 100 ml round-bottomed flask, a mixture of (6 ml) of 15% alcoholic sodium hydroxide solution, (25 ml) of ethanol (0.005 mole) of acetone was stirred magnetically for (5 min). A(0.005 mole) of desired Chalcone was added dropwise through a dropping funnel. Stirring was contained for (45-90) min. at (20-60)C o till the reaction showed no further change in colour. The reaction mixture was distilled to remove the solvent. The residual coloured product was examined by spectral and physical analysis. The physical properties and some spectral data were illustrated on Table-3, Table-
The IR spectrum (25) showed a strong sharp signal at (1640-1648) cm -1 attributed to the carbonyl group, while the signal at (1600) cm -1 is related to the stretching vibration of the carbon-carbon double bond (γ C=C). The signal at (1528) cm -1 belong to C C (aromatic character), Where asymmetric and symmetric streching of N O group (of the nitro group) seemed at 1441 and 1349 cm -1 respectively. Finally, the ethereal group C-O-C assigned at 1245 cm -1 .
The UV spectrum (26) manifested a maximum absorbance at a wavelength of (246-330) nm which reflects blue shift when compared with the ranges of starting materials (284-380) nm (Table-2).
The suggested mechanism for the reaction of Chalcone with acetone may be shown at Scheme -1.
The strong basic condition causes the abstraction of an acidic proton from an acetone molecule to give the corresponding anion(A). The anion (A) may attack the Chalcone in two probable and different ways, either added to the β-carbon (Michael addition or 1,4-addition) or added to the carbonyl carbon (Claisn addition or 1,2-addition).

Michael route:
If the anion (A) attacks the β-carbon, it will afford the intermediate

Claisn route:
The anion (A) attacks the carbonyl carbon to give the intermediate (C