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N-Heterocyclic carbene-catalyzed oxidative [3 + 2] annulation of dioxindoles and enals: cross coupling of homoenolate and enolate † † Electronic supplementary information (ESI) available: Experimental procedures and compound characterizations (PDF). CCDC 1041425 ( 3fb ). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc04135c Click here for additional data file. Click here for additional data file.

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ABSTRACT

The N-heterocyclic carbene-catalyzed oxidative [3 + 2] annulation of dioxindole and enals was developed, giving the corresponding spirocyclic oxindole-γ-lactones in good yields with high to excellent diastereo- and enantioselectivities. The challenging aliphatic enals worked effectively using this strategy. The oxidative cross coupling of homoenolate and enolate via single electron transfer was proposed as the key step for the reaction.

No MeSH data available.


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Oxidative NHC-catalyzed transformations of enals.
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sch1: Oxidative NHC-catalyzed transformations of enals.

Mentions: Initiated half century ago,3 N-heterocyclic carbene (NHC) catalysis has witnessed great success in recent years.4 In 2004, Bode et al. and Glorius et al. reported the elegant NHC-catalyzed reaction of enals involving homoenolate as the key intermediate (Scheme 1, reaction a).5 The homoenolate intermediate could be oxidized to give α,β-unsaturated acyl azolium, which worked as a versatile 1,3-biselectrophile (Scheme 1, reaction b).6 Single electron oxidation could open new ways for organic reactions. In 2008, Studer et al.7 reported the NHC-catalyzed conversion of enals to esters using TEMPO as a single-electron oxidant (Scheme 1, reaction c). During our investigation of this work, the single electron oxidation of the homoenolate was pioneered by Rovis et al.8 and Chi et al.9 (Scheme 1, reaction d). The oxidative homo and cross-coupling of the two homoenolates was established by Rovis et al. (Scheme 1, reaction e).10 In this paper, we demonstrated that the challenge of the cross-coupling of homoenolate and enolate was solved well when a proper oxidant and proper enolates were employed (Scheme 1, reaction f).


N-Heterocyclic carbene-catalyzed oxidative [3 + 2] annulation of dioxindoles and enals: cross coupling of homoenolate and enolate † † Electronic supplementary information (ESI) available: Experimental procedures and compound characterizations (PDF). CCDC 1041425 ( 3fb ). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc04135c Click here for additional data file. Click here for additional data file.
Oxidative NHC-catalyzed transformations of enals.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384455&req=5

sch1: Oxidative NHC-catalyzed transformations of enals.
Mentions: Initiated half century ago,3 N-heterocyclic carbene (NHC) catalysis has witnessed great success in recent years.4 In 2004, Bode et al. and Glorius et al. reported the elegant NHC-catalyzed reaction of enals involving homoenolate as the key intermediate (Scheme 1, reaction a).5 The homoenolate intermediate could be oxidized to give α,β-unsaturated acyl azolium, which worked as a versatile 1,3-biselectrophile (Scheme 1, reaction b).6 Single electron oxidation could open new ways for organic reactions. In 2008, Studer et al.7 reported the NHC-catalyzed conversion of enals to esters using TEMPO as a single-electron oxidant (Scheme 1, reaction c). During our investigation of this work, the single electron oxidation of the homoenolate was pioneered by Rovis et al.8 and Chi et al.9 (Scheme 1, reaction d). The oxidative homo and cross-coupling of the two homoenolates was established by Rovis et al. (Scheme 1, reaction e).10 In this paper, we demonstrated that the challenge of the cross-coupling of homoenolate and enolate was solved well when a proper oxidant and proper enolates were employed (Scheme 1, reaction f).

View Article: PubMed Central - PubMed

ABSTRACT

The N-heterocyclic carbene-catalyzed oxidative [3 + 2] annulation of dioxindole and enals was developed, giving the corresponding spirocyclic oxindole-γ-lactones in good yields with high to excellent diastereo- and enantioselectivities. The challenging aliphatic enals worked effectively using this strategy. The oxidative cross coupling of homoenolate and enolate via single electron transfer was proposed as the key step for the reaction.

No MeSH data available.


Related in: MedlinePlus