Preparation of 4,6-Disubstituted α-Pyrones by Oxidative N-Heterocyclic Carbene Catalysis

Dedicated to Prof. Dieter Enders, a pioneer and driving force in carbene catalysis, on the occasion of his 70^th birthday

Abstract

An efficient synthesis of 4,6-disubstituted α-pyrones employing redox activation of enals using N-heterocyclic carbene catalysis is reported. The strategy uses aroyl-substituted nitromethanes and enals as substrates and reactions proceed through an addition–elimination–lactonization sequence. On one hand the nitro group in the starting ketone stabilizes the enolate and on the other hand it also acts as an ionic leaving group. Products are obtained in moderate to good yields.

Key words

α-pyrone - N-heterocyclic carbine - oxidative organocatalysis - NHC catalysis - elimination - lactonization

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• 13 It is also possible that the intermediate 6 may undergo intramolecular proton transfer to give a ketone enolate which then lactonizes to the corresponding dihydropyranone. Subsequent double bond isomerization and HNO₂ elimination will afford α-pyrone 4 (Scheme 4). We thank a reviewer for this valuable suggestion.