Catalytic Asymmetric Intramolecular [4+2] Cycloaddition of In Situ Generated <i>ortho</i>‐Quinone Methides

Xie, Youwei; List, Benjamin

doi:10.1002/anie.201612149

Cited by 126 publications

(34 citation statements)

References 99 publications

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“…To extend the scope of the reaction, it was also attempted on an o-quinone methide generated in situ, and it proceeded smoothly, but with a decrease of both yield and enantioselectivity. o-Quinone methides can be also obtained from salicylaldehydes and they were allowed to react with unsaturated alcohols to give furano-and pyrano-chromanes (Scheme 30) [45]. The absolute configuration of products was determined by X-ray analysis.…”

Section: Cycloaddition Of Ortho-quinone Methidesmentioning

confidence: 99%

“…The isomerization energy was calculated by DFT and was found to be very low (7.0 kcal/mol) [46], so that all papers generally explained the observed stereochemistry with both mechanisms. o-Quinone methides can be also obtained from salicylaldehydes and they were allowed to react with unsaturated alcohols to give furano-and pyrano-chromanes (Scheme 30) [45]. The absolute configuration of products was determined by X-ray analysis.…”

Section: Cycloaddition Of Ortho-quinone Methidesmentioning

confidence: 99%

“…Some experiments were carried out to elucidate the mechanism and the result seems to be consistent with a [4+2] addition, but the authors did not rule out a stepwise mechanism. o-Quinone methides can be also obtained from salicylaldehydes and they were allowed to react with unsaturated alcohols to give furano-and pyrano-chromanes (Scheme 30) [45]. The absolute configuration of products was determined by X-ray analysis.…”

Section: Cycloaddition Of Ortho-quinone Methidesmentioning

confidence: 99%

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Recent Advances in Organocatalyzed Asymmetric Synthesis of Benzopyran and Benzodihydropyran (Chromane) Nuclei

Dalpozzo

Mancuso

2019

Symmetry

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Benzopyran and benzodihydropyran (chromane) nuclei are the core structure of many natural products, in particular flavonoids. Many compounds possessing this structure are nutraceuticals, pharmaceutical nutrients. Therefore, benzopyran and chromane scaffolds are important building blocks in organic synthesis and many efforts have been made to set up efficient methods for their synthesis. In particular, asymmetric methods are of great importance, being natural products, and generally chiral substances. This review aims to cover literature in the range 2017-first half of 2019.It should be noted that the oxa-Michael-Henry reaction between two molecules of nitrostyrene was not observed. Symmetry 2020, 12, x FOR PEER REVIEW 4 of 33 Scheme 2. Heterogeneous enantioselective synthesis of chromanes.Xia, Xu and co-workers performed an enantioselective, organocatalytic oxa-Michael-nitro-Michael reaction, but in this case, too, 2-hydroxynitrostyrenes reacted only with β-nitroolefins different from themselves [10]. The reaction afforded chiral chromane derivatives bearing three contiguous stereogenic centers (Scheme 3). The all-S stereochemistry was assigned by X-ray analysis. Subsequently, Andrés, Pedrosa and co-workers extended the reaction to polymer-supported squaramides [11]. Initially, they tested some 4-vinylphenyl-substituted squaramides and found that Squa2 (see Scheme 1, 5 mol%, rt, 12-72 h in dichloromethane) gave the best results (65-88% yields, 63:27 to >99:1 dr, 70-> 99% ee, 13 examples). The absolute configuration was once more (2S,3S,4S) and was established by X-ray analysis. The configuration of the minor isomer was instead established as (2S,3R,4S) by comparison of the 1 H-NMR coupling constants of the two diastereomers. Then Squa2 was co-polymerized with styrene and divinylbenzene and the experiments were repeated (65-86% yields, 58:42 to >99:1 dr, 56-74% ee). The polymer-supported catalyst was also recovered and recycled five times without affecting yields and selectivity. Finally, the enantiomers were obtained from a squaramide derived from (1R,2R)-1,2-cyclohexanediamine instead of Squa2 derived from α-amino acid. The authors attributed the opposite stereochemistry to a different assembly of the ternary complex formed by catalyst, nitroalkene and 2-hydroxynitrostyrene in the two cases. S O HN HO HO OHC Symmetry 2019, 11, 1510 5 of 31 Symmetry 2020, 12, x FOR PEER REVIEW 5 of 33 Scheme 3. Organocatalytic oxa-Michael nitro-Michael domino reaction.Another domino Michael/hemiacetalization (see also Scheme 2, eq 3) was carried out between aliphatic aldehydes and (E)-2-(2-nitrovinyl)phenols under modularly designed organocatalysts (Scheme 4) [12]. Cis-3,4-disubstituted chroman-2-ones were obtained after oxidation of the hemiacetal intermediate or chromanes after dehydroxylation. The reaction was scaled up to 0.5 mmol scale, without significant modification of yield and selectivity. The absolute stereochemistry was determined by the optical rotation of known compounds. Scheme 4. Domino reaction catalyzed by MDO o...

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Section: Cycloaddition Of Ortho-quinone Methidesmentioning

confidence: 99%

Section: Cycloaddition Of Ortho-quinone Methidesmentioning

confidence: 99%

Section: Cycloaddition Of Ortho-quinone Methidesmentioning

confidence: 99%

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Recent Advances in Organocatalyzed Asymmetric Synthesis of Benzopyran and Benzodihydropyran (Chromane) Nuclei

Dalpozzo

Mancuso

2019

Symmetry

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“…In the past decades,o rganocatalytic [4+ +2] cycloadditions [4] were one of the most widely used synthetic methods for the synthesis of simple and complex ring systems.Among the reported examples,a symmetric [4+ +2] cycloaddition between ortho-quinone methides (o-QMs) [5] and olefins represents one of the most direct and expedient approaches for constructing oxygen-containing heterocycles.G reat achievements in the field of intermolecular [4+ +2] cycloadditions were made by the groups of Sun, [6] Rueping, [7] Shi [8] et al [9] Recently,L ist and co-workers [10] reported the first imidodiphosphoric acid-catalyzed [11] intramolecular [4+ +2] cycloaddition of in situ generated o-QMs (Scheme 1). Compared with the wide application of o-QMs in asymmetric synthesis, vinylidene ortho-quinone methide (VQM), [12] av ariant of o-QMs,h as been seldom explored.…”

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confidence: 99%

Organocatalytic Intramolecular [4+2] Cycloaddition between In Situ Generated Vinylidene ortho‐Quinone Methides and Benzofurans

Xue

et al. 2017

Angew Chem Int Ed

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Described herein is the enantioselective construction of oxygen-containing [5-6-5] tricyclic heterocycles by an organocatalyzed asymmetric [4+2] cycloaddition of vinylidene ortho-quinone methides and benzofurans. According to this methodology, a series of oxygen-containing [5-6-5] tricyclic heterocycles with various functional groups were synthesized in excellent enantio- and diastereoselectivities (>99 % ee, >20:1 d.r.). Furthermore, the deuterium-labeling experiments and high-resolution mass spectroscopy demonstrated that a vinylidene ortho-quinone methide intermediate was involved and possibly resulted from a prototropic rearrangement of 2-ethynylphenol. Remarkably, a catalyst loading as low as 0.1 mol %, and a gram-scale synthesis were achieved for this transformation.

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“…Die Bestimmung der absoluten Konfiguration des Produktes 3h erfolgte eindeutig durch Rçntgenstrukturanalyse und die der anderen Produkte in Analogie dazu (Tabelle 1u nd Abbildung S1). [17] Wiru ntersuchten auch mehrere Dienylalkohole mit unterschiedlichen Substitutionsmustern (Tabelle 2 Ein Reaktionsmechanismus fürd ie Reaktion von Salicylaldehyd (1a)m it Alkohol 2,k atalysiert durch die abgeschirmte Säure 4b,w ird in Schema 3v orgeschlagen. Nach einer Kondensation unter Wasserspaltung der beiden Ausgangsmaterialien wird Oxocarbenium-Ion I,e ine Resonanzstruktur des ortho-Chinonmethids II,gebildet.…”

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Katalytisch‐asymmetrische intramolekulare [4+2]‐Cycloaddition von in situ generierten ortho‐Chinonmethiden

Xie

List

2017

Angewandte Chemie

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Die erste katalytisch-asymmetrische intramolekulare [4 + 2]-Cycloaddition von in situ generierten ortho-Chinonmethiden wurde entwickelt. Katalysiert durch eine abgeschirmte chirale Imidodiphosphorsäure,r eagieren diverse Salicylaldehyde mit Dienylalkoholen zu kurzlebigen ortho-Chinonmethid-Intermediaten, die durchi ntramolekulare [4 + 2]-Cycloaddition zu hochf unktionalisierten Furan-und Pyranchromanen mit exzellenten Diastereo-und Enantioselektivitäten umgewandelt werden.

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Catalytic Asymmetric Intramolecular [4+2] Cycloaddition of In Situ Generated ortho‐Quinone Methides

Cited by 126 publications

References 99 publications

Recent Advances in Organocatalyzed Asymmetric Synthesis of Benzopyran and Benzodihydropyran (Chromane) Nuclei

Recent Advances in Organocatalyzed Asymmetric Synthesis of Benzopyran and Benzodihydropyran (Chromane) Nuclei

Organocatalytic Intramolecular [4+2] Cycloaddition between In Situ Generated Vinylidene ortho‐Quinone Methides and Benzofurans

Katalytisch‐asymmetrische intramolekulare [4+2]‐Cycloaddition von in situ generierten ortho‐Chinonmethiden

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