Addition to Chalcone in a Water Suspension Medium

13 Michael Addition to Chalcone in a Water Suspension Medium 

Very efficient Michael addition reactions of amines, thiophenoi and acetylacetate to chalcone in a water suspension medium have been developed as completely organic solvent-free reactions. 

As a typical example of Michael addition of an amine to chalcone in a water suspension medium, a suspension of powdered chalcone (70a) in a small amount of water containing mBuNH2 (71e) and the surfactant hexadecyltrimethylammo-nium bromide (72) was stirred at room temperature for 4 h. The reaction product was filtered and air dried to give the Michael addition product 73e as a colorless powder in 98% yield. The filtrate containing 72 can be used again [34]. By the same procedure, Michael addition reactions of the various amines 71a-q to 70a were carried out and pure amineadducts were obtained in good yields (Table 15-19) [34], The solubility of the amines in water is not related to the efficiency of the reaction. Amines (71h-k) which are poorly soluble in water reacted with 70a in the water suspension as effectively as the water-soluble amines (Table 15-19). 

These Michael adducts cannot be obtained in a pure state through reaction in organic solvents. For example, when a solution of 70a and 71e in toluene was stirred at room temperature and solvent evaporated below 40°C in vacuo, a mixture of 73e and 70a was obtained as an oily material which contained 73e in only 

38% yield ( H NMR analysis in CDCI3). Furthermore, because of the equilibrium in solution, it is difficult to isolate 73 in a pure state from the mixture. For example, H NMR spectral analysis showed that a solution of pure 73e (0.1 g) in toluene (1 ml) consists of 53% of 73e and 47% of 70a. As far as we are aware, only 73n has been prepared previously in a pure crystalline state by the reaction of 70a and 71n in a sealed tube at 100 C [34]. 

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