Limits...
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.

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.


Plausible catalytic cycle.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5384455&req=5

fig1: Plausible catalytic cycle.

Mentions: Based on the control experiments and EPR signals observed, we propose a radical/radical cross-coupling pathway for this NHC-catalyzed oxidative [3 + 2] annulation reaction of dioxindoles and enals (Fig. 1). Firstly, the addition of NHC to enals gives the corresponding Breslow intermediate I, which is partially oxidized to the radical cation intermediate II in the presence of nitrobenzene as the single electron oxidant.8,17 In the meantime, the generated radical anion III could abstract a hydrogen from dioxindole 2 to give its enolate radical IV. The cross-coupling of the enolate radical II and the homoenolate radical IV affords adduct V, which is tautomerized to γ-hydroxy acylazolium VI. The lactonization of acyl azolium VI under basic conditions gives the final cycloadduct 3 and regenerates the NHC catalyst.


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.
Plausible catalytic cycle.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: Plausible catalytic cycle.
Mentions: Based on the control experiments and EPR signals observed, we propose a radical/radical cross-coupling pathway for this NHC-catalyzed oxidative [3 + 2] annulation reaction of dioxindoles and enals (Fig. 1). Firstly, the addition of NHC to enals gives the corresponding Breslow intermediate I, which is partially oxidized to the radical cation intermediate II in the presence of nitrobenzene as the single electron oxidant.8,17 In the meantime, the generated radical anion III could abstract a hydrogen from dioxindole 2 to give its enolate radical IV. The cross-coupling of the enolate radical II and the homoenolate radical IV affords adduct V, which is tautomerized to γ-hydroxy acylazolium VI. The lactonization of acyl azolium VI under basic conditions gives the final cycloadduct 3 and regenerates the NHC catalyst.

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.