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. 2015 Feb 25;51(16):3407-10.
doi: 10.1039/c4cc09590a.

N-Heterocyclic carbene-catalyzed enantioselective annulations: a dual activation strategy for a formal [4+2] addition for dihydrocoumarins

Anna Lee  1 , Karl A Scheidt
Affiliations

N-Heterocyclic carbene-catalyzed enantioselective annulations: a dual activation strategy for a formal [4+2] addition for dihydrocoumarins

Anna Lee et al. Chem Commun (Camb). .

Abstract

A highly efficient asymmetric formal [4+2] annulation for the synthesis of dihydrocoumarins has been developed via an in situ activated NHC catalysis. Both electrophilic and nucleophilic species are generated in situ simultaneously whereby acyl imidazoles facilitated rapid formation of an NHC-enolate intermediate to afford the [4+2] dihydrocoumarin adducts.

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Figures

Figure 1
Figure 1
Racemization in the presence of 1.0 equiv. of CsOAc as the base (Table 1, entry 3).
Scheme 1
Scheme 1
Dual activation NHC strategy.
Scheme 2
Scheme 2
Proposed Reaction Pathways.
See this image and copyright information in PMC

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