Taking into account the postulated reaction mechanism for the organocatalytic epoxidation of electron-poor olefins developed by our laboratory, we have investigated the key factors able to positively influence the H-bond network installed inside the substrate/catalyst/oxidizing agent. With this aim, we have: (i) tested a few catalysts displaying various effects that noticeably differ in terms of steric hindrance and electron demand; (ii) employed alpha-alkylidene oxindoles decorated with different substituents on the aromatic ring (11a-“g), the exocyclic double bond (11h-l), and the amide moiety (11m-“v). The observed results suggest that the modification of the electron-withdrawing group (EWG) weakly conditions the overall outcomes, and conversely a strong influence is unambiguously ascribable to either the N-protected or N-protected lactam framework. Specifically, when the NH free substrates (11m-“u) are employed, an inversion of the stereochemical control is observed, while the introduction of a Boc protecting group affords the desired product 12v in excellent enantioselectivity (97:3 er).

Miceli, M., Mazziotta, A., Palumbo, C., Roma, E., Tosi, E., Longhi, G., et al. (2018). Asymmetric synthesis of spirooxindoles via nucleophilic epoxidation promoted by bifunctional organocatalysts. MOLECULES, 23(2), 438 [10.3390/molecules23020438].

Asymmetric synthesis of spirooxindoles via nucleophilic epoxidation promoted by bifunctional organocatalysts

Miceli, Martina
Membro del Collaboration Group
;
Mazziotta, Andrea
Membro del Collaboration Group
;
Roma, Elia
Membro del Collaboration Group
;
Gasperi, Tecla
Membro del Collaboration Group
2018

Abstract

Taking into account the postulated reaction mechanism for the organocatalytic epoxidation of electron-poor olefins developed by our laboratory, we have investigated the key factors able to positively influence the H-bond network installed inside the substrate/catalyst/oxidizing agent. With this aim, we have: (i) tested a few catalysts displaying various effects that noticeably differ in terms of steric hindrance and electron demand; (ii) employed alpha-alkylidene oxindoles decorated with different substituents on the aromatic ring (11a-“g), the exocyclic double bond (11h-l), and the amide moiety (11m-“v). The observed results suggest that the modification of the electron-withdrawing group (EWG) weakly conditions the overall outcomes, and conversely a strong influence is unambiguously ascribable to either the N-protected or N-protected lactam framework. Specifically, when the NH free substrates (11m-“u) are employed, an inversion of the stereochemical control is observed, while the introduction of a Boc protecting group affords the desired product 12v in excellent enantioselectivity (97:3 er).
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11590/331022
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