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2.8.1.2 Stetter Reaction

DOI: 10.1055/sos-SD-224-00223

Davies, A. T.; Smith, A. D.Science of Synthesis: N-Heterocyclic Carbenes in Catalytic Organic Synthesis, (20162399.

Despite the benzoin condensation having been known since the 19th century, the addition of an acyl anion equivalent to an α,β-unsaturated carbonyl compound was not reported until 1973 by Stetter and Schreckenberg.[‌43‌] Whilst the initial work utilized a cyanide anion as the catalyst, further work from Stetter and Kuhlmann in 1974 showed the ability of thiazolylidene catalysts to promote the reaction.[‌44‌] As a result of this discovery and extensive examination of the system, this process has since become known as the Stetter reaction. Asymmetric intramolecular variants have been developed by the groups of Enders and Rovis amongst others, with catalyst structures employed similar to those which proved so successful in the development of the asymmetric benzoin condensation. Asymmetric intermolecular examples have proved much more elusive, particularly with respect to substrate generality. The first published example was reported by Enders in 1993, obtaining a modest enantiomeric ratio of 70:30,[‌45‌] and subsequent work from the groups of Rovis,[‌46‌] utilizing glyoxamides and highly reactive Michael acceptors with chiral triazolium tetrafluoroborate salt 9, and Enders,[‌47‌] using benzaldehydes and chalcones with chiral triazolium tetrafluoroborate salt 10, produced optimal enantiomeric ratios of 96:4 and 89:11, respectively (Scheme 5).

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