Marcus Blümel

Asymmetric Synthesis of Spirobenzazepinones with Atroposelectivity and Spiro-1,2-Diazepinones by NHC-Catalyzed [3+4] Annulation Reactions

A strategy for the NHC-catalyzed asymmetric synthesis of spirobenzazepinones, spiro-1,2-diazepinones, and spiro-1,2-oxazepinones has been developed via [3+4]-cycloaddition reactions of isatin-derived enals (3C component) with in-situ-generated aza-o-quinone methides, azoalkenes, and nitrosoalkenes (4atom components). The [3+4] annulation strategy leads to the seven-membered target spiro heterocycles bearing an oxindole moiety in high yields and excellent enantioselectivities with a wide variety of substrates. Notably, the benzazepinone synthesis is atroposelective and an all-carbon spiro stereocenter is generated.

Asymmetric synthesis of tetrahydropyridines via an organocatalytic one-pot multicomponent Michael/aza-Henry/cyclization triple domino reaction.

A low loading of a quinine-derived squaramide efficiently catalyzes the triple-domino Michael/aza-Henry/cyclization reaction between 1,3-dicarbonyl compounds, β-nitroolefins, and aldimines to provide tetrahydropyridines bearing three contiguous stereogenic centers in good yields, excellent enantiomeric excesses, and up to high diastereomeric ratios.

Development and Applications of Transesterification Reactions Catalyzed by N-Heterocyclic Olefins

A novel method to utilize N-heterocyclic olefins (NHOs), the alkylidene derivatives of N-heterocycic carbenes, as organocatalysts to promote transesterification reactions has been developed. Because of their strong Brønsted/Lewis basicity, NHOs can enhance the nucleophilicity of alcohols for their acylation reactions with carboxylic esters. This transformation can be employed in industrially relevant processes such as the production of biodiesel, the depolymerization of polyethylene terephthalate (PET) from plastic bottles for recycling purposes, and the ring-opening polymerization of cyclic esters to form biodegradable polymers such as polylactide (PLA) and polycaprolactone (PCL).

Switchable Access to Different Spirocyclopentane Oxindoles by N-Heterocyclic Carbene Catalyzed Reactions of Isatin-Derived Enals and N-Sulfonyl Ketimines

A novel NHC-catalyzed annulation protocol for the asymmetric synthesis of biologically important β-lactam fused spirocyclopentane oxindoles with four contiguous stereocenters, including two quaternary carbon centers, was developed. Alternatively, spirocyclopentane oxindoles containing an enaminone moiety can be achieved using the same starting materials, isatin-derived enals, and N-sulfonyl ketimines, in the presence of a slightly different NHC catalytic system. This switchable annulation strategy enables the selective assembly of both heterocyclic scaffolds with good yields and excellent enantioselectivities for a broad range of substrates.

NHC‐Catalyzed Asymmetric Synthesis of Functionalized Succinimides from Enals and α‐Ketoamides

The efficient asymmetric synthesis of highly substituted succinimides from α,β-unsaturated aldehydes and α-ketoamides via NHC-catalyzed [3+2] cycloaddition has been developed. The new scalable protocol significantly expands the utility of NHC catalysis for the synthesis of heterocycles and provides easy access to assemble a wide range of succinimides from simple starting materials.

Promotion of Organic Reactions by Non-Benzenoid Carbocyclic Aromatic Ions

The first three primary members of the non-benzenoid carbocyclic aromatic ion family, namely cyclopropenium, cyclopentadienide, and cycloheptatrienium (tropylium) ions, have planar cyclic structures with (4n+2)π electrons in fully conjugated systems. They fulfill Hückels rule for aromaticity and hence possess extraordinary stability. Since the historic discovery of tropylium bromide in the late 19th Century, these non-benzenoid aromatic ions have attracted a lot of attention because of their unique combination of stability and reactivity. The charge on the aromatic ions makes them more prone to nucleophilic/electrophilic reactions than the neutral benzenoid counterparts. Within the last seven years, there has been a large number of investigations in utilizing aromatic ions to mediate organic reactions. This Review highlights these recent developments and discusses the potential of aromatic ions in promoting synthetically useful organic transformations.