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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
N-Heterocyclic Carbene Catalyzed (5+1) Annulations Exploiting a Vinyl Dianion Synthon Strategy
Xuan B Nguyen1, Yuji Nakano1, Nisharnthi M Duggan1
1School of Chemistry, Monash University, Clayton, 3800, Victoria, Australia.
Abstract:
Direct polarity inversion of conjugate acceptors provides a valuable entry to homoenolates. N-heterocyclic carbene (NHC) catalyzed reactions, in which β-unsubstituted conjugate acceptors undergo homoenolate formation and C-C bond formation twice, have been developed. Specifically, the all-carbon (5+1) annulations give a range of mono- and bicyclic cyclohexanones (31 examples). In the first family of annulations, β-unsubstituted acrylates tethered to a divinyl ketone undergo cycloisomerization, providing hexahydroindenes and tetralins. In the second, partially untethered substrates undergo an intermolecular (5+1) annulation involving dimerization followed by cycloisomerization. While enantioselectivity was not possible with the former, the latter proved viable, allowing cyclohexanones to be produced with high levels of enantiopurity (most >95:5 e.r.) and exclusive diastereoselectivity (>20:1 d.r.). Derivatizations and mechanistic studies are also reported.
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5-Number Summary
In a box plot, the minimum and maximum data values represent the lower and upper whiskers in the graph, and the median is designated as the center of the box in the chart. The first quartile and third...

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