N-heterocyclic carbene catalyzed reactions of α,β-unsaturated aldehydes and a variety of electrophiles allow the facile preparation of a diverse array of annulation products including trisubstituted cyclopentenes, γ-lactams, and bicyclic β-lactams. The substrate scope of these reactions, however, is limited by the difficulties of preparing the startingα,β-unsaturated aldehydes. We now report that α′-hydroxyenones, which can be prepared in a single convenient step from aromatic and heteroaromatic aldehydes, can serve as efficient surrogates for enals in the annulation reactions. This protocol allows the facile preparation and use of substrates bearing nitrogen heterocycles. These reagents have also allowed us to demonstrate that, in contrast to other classes of aldehydes, the formation of the Breslow intermediate from enals and N-heterocyclic carbenes is irreversible under the reaction conditions.

Cyclic sulfonyl imines derived from ketones were identified as stable and readily prepared compounds that serve as superior electrophiles for N-heterocyclic carbene (NHC)-catalyzed annulations with α,β-unsaturated aldehydes to afford highly substituted γ-lactams. Their superior reactivity and properties are highlighted by the first example of NHC-catalyzed reactions of enals with low catalyst loadings (0.5 mol %) and broad substrate scope encompassing alkyl, aryl, and heteroaromatic substituents. These findings and supporting studies suggest an alternative, ene-like mechanism rather than the catalytic generation of a catalyst-bound homoenolate equivalent.

Efficient syntheses of three novel scaffolds for potential β-glycosidase inhibitors were developed: The first consists of a 2,7-dioxabicyclo[2.2.1]heptane derivative, which was prepared by an intramolecular ketalisation. The second scaffold consists of a hydroxylated cyclopentylamine, which could be synthesised stereoselectively from 2-azabicyclo[2.2.1]hept-5-en-3-one. The third scaffold, a 4,5-dihydroxynicotinic acid,

A synthetic access to biologically active (.+‐.)‐clausenamide (V) is given.

Ring closure reactions O 0130 α'-Hydroxyenones as Mechanistic Probes and Scope-Expanding Surrogates for α,β-Unsaturated Aldehydes in N-Heterocyclic Carbene-Catalyzed Reactions.α'-Hydroxyenones are useful substrates in triazolium-catalyzed annulation reactions affording trisubstituted cyclopentenes, γ-lactams, and bicyclic β-lactams. The main advantage lies in their facile preparation and handling in a single step from commercial materials. Other advantages are cleaner reactions by avoiding or diminishing side reactions such as decomposition or dimerization of the aldehydes. -(CHIANG, P.-C.; ROMMEL, M.; BODE*,