Highly Enantioselective Nitroaldol Reactions Catalyzed by Copper(II) Complexes Derived from Substituted 2-(Pyridin-2-yl)imidazolidin-4-one Ligands

Abstract

Ten optically pure substituted 2-(pyridin-2-yl)imidazolidin-4-ones, 1a-d, 2a-4a, and 2b-4b, were prepared and characterized. The absolute configurations of individual ligands were determined by X-ray analysis or NOESY experiments. The Cu(II) complexes of the respective ligands were studied as enantioselective catalysts of the nitroaldol (Henry) reaction of aldehydes with nitromethane, giving the corresponding substituted 2-nitroalkanols. In the case of an anti arrangement of the imidazolidin-4-one ring, the obtained result was 91-96% ee, whereas in the case of syn arrangement, a significant drop to 25-27% ee was observed.

Recyclable Enantioselective Catalysts Based on Copper(II) Complexes of 2‐(Pyridine‐2‐yl)imidazolidine‐4‐thione: Their Application in Asymmetric Henry Reactions

“…With regard to the confirmed higher catalytic activity of heterogeneous catalysts 7 – 9 , in the subsequent study, we tested their enantioselectivity in the Henry reaction at the temperature of −10 °C (Table ). From the ee values found (∼90%) it is obvious that the enantioselectivity of catalysts Cu(OAc) 2 / 3a‐b and 7–9 increased (under these reaction conditions) up to the level comparable with that of the homogeneous catalyst Cu(OAc) 2 / 2a‐b (Table ), and/or with the earlier prepared catalyst based on 2‐(pyridine‐2‐yl)imidazolidine‐4‐one . The conversion values at this lower temperature remained very high (72–99%).…”

“…Whereas the catalysis with complex of (2 R ,5 S )‐ 2a gave the corresponding 2‐nitroethanols with the R‐ configuration in excess, the application of complex of (2 S ,5 S )‐ 2b gave the products with the S‐ configuration in excess. The ee values of products show that the enantioselectivity of copper(II) complex of ligand 2a is high (88–97% ee ) and comparable with that of the analogous complex of (2 R ,5 S )‐5‐isopropyl‐2,5‐dimethyl‐2‐(pyridine‐2‐yl)imidazolidine‐4‐one . Also the conversion values under the given conditions were high (67–99%).…”

“…Also the conversion values under the given conditions were high (67–99%). Surprisingly, the copper(II) complex of the cis ‐form of the ligand [Cu(OAc) 2 / 2b ] also exhibited a high enantioselectivity (70–94% ee ), whereas the oxygen analogue (derivative of imidazolidine‐4‐one) did not reach such satisfactory results (for benzaldehyde 23% ee ) . In the case of aromatic aldehydes containing electron‐donating groups (experiments 1, 2, 5 and 7) with the application of complex Cu(OAc) 2 / 2b , the attained enantioselectivity was higher (84–87% ee ) than that obtained with aldehydes containing electron‐withdrawing groups (experiments 3 and 4; 75% and 70% ee , respectively).…”

“…Their high enantioselectivity classifies them as the best so far known enantioselective recyclable catalysts for the Henry reaction . Two further reactions performed in the case of the synthesis of immobilized catalysts 7 – 9 , namely the thionation of the starting ( S )‐2‐amino‐2,3‐dimethylbutaneamide giving ( S )‐2‐amino‐2,3‐dimethylbutanethioamide ( 1 ) (72%) and anchoring of ligands 2a‐b on polymeric carriers (82–99%), led to a lowering of the total yield of this synthetic procedure as compared with the yield of the synthesis of the original catalyst based on 2‐(pyridine‐2‐yl)imidazolidine‐4‐one derivative . On the other hand, the immobilized catalysts 7–9 can be recovered and reused more than ten times and thus they are more advantageous not only economically, but their application is also more environment‐friendly.…”

Imidazolidinones and Imidazolidine‐2,4‐diones as Antiviral Agents

“…[21][22][23] Conventionally,2 -imidazolidinones and other cyclic ureas are synthesized by the reaction of diamines with several reagents such as carbonyldiimidazole, [24] trichloromethyl chloroformate, [25] organic carbonates, [26,27] dithiocarbonate, [28] carbonyl selenide, [29,30] and carbon monoxide (Scheme 1). [31,32] The reported methods for the synthesis of 4-imidazolidinones are reactiono fg lycinamide derivatives with carbonyl compounds under acidic [33,34] and basic [35,36] conditions (Scheme 2).…”