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, MartinaMembro del Collaboration Group
;Mazziotta, AndreaMembro del Collaboration Group
;Roma, EliaMembro del Collaboration Group
;Gasperi, Tecla
Membro del Collaboration Group
2018-01-01
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).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
