2015

Abstract:

An enantio-, diastereo-, regio-, and chemoselective phosphine-catalyzed β,γ-umpolung domino reaction of allenic esters with dienones has been developed for the first time. The designed sequence, involving oxy-Michael and Rauhut–Currier reactions, produced highly functionalized tetrahydrobenzofuranones, bearing a chiral tetrasubstituted stereogenic center, in up to 96 % ee.

Abstract:

Aza-ortho-quinone methides allow the straightforward asymmetric synthesis of natural-product-inspired indole scaffolds possessing a quaternary stereocenter. Our approach provides access to diverse communesin and spiroindoline derivatives with high enantioselectivity under mild reaction conditions. Predictable substitution patterns are found to be the key to our regiodivergent protocols.

Abstract:

Phosphoric acids have emerged as efficient organo-catalysts for various reactions. Despite widespread use, details of the reaction intermediates giving rise to stereocontrol have remained elusive. To clarify the nature of the catalyst–substrate interaction, we characterize and quantify catalyst–substrate complex formation by combining dielectric spectroscopy, quantum chemistry, and 1H NMR spectroscopy. For a series of different solvents, the interaction between substrate and catalyst is dominated by ion-pairing, rather than hydrogen bonding, at ambient conditions. Correlation of ion association with catalytic enantioselectivity provides evidence that close-contact ion-pairing is essential for stereocontrol and that dissociation into free ions dramatically reduces enantioselectivity.

Abstract:

Ketyl radical and amino radical anions, valuable reactive intermediates for C=C bond-forming reactions, are accessible through a C=O/C=NR umpolung. However, their utilization in catalysis remains largely underdeveloped owing to the high reduction potential of carbonyl compounds and imines. In the context of photoredox catalysis, tertiary amines are commonly employed as sacrificial co-reducing agents. Herein, an additional role of the amine is proposed, in which it is essential for the organocatalytic substrate activation. The combination of photoredox catalysis and carbonyl/imine activation enables the reductive coupling of aldehydes, ketones, and imines under mild reaction conditions.

Abstract:

The direct arylation of heteroaromatics with an easily accessible and recyclable, heterogeneous TiO2 catalyst and visible light was developed. Electron-rich as well as electron-poor heteroarenes could be applied in this transformation, and the corresponding products were isolated in very good yields. Azoethers were detected as reactive intermediates, and the unexpected role of TiO2 in their formation as well as reaction was established.

Abstract:

An efficient method for the highly enantioselective synthesis of chiral chromanes bearing multiple stereogenic centers was developed. A chiral BINOL-based N-triflylphosphoramide proved to be an effective catalyst for the in situ generation of ortho-quinone methides (o-QMs) and their subsequent cycloaddition reaction with unactivated alkenes provided chromanes with excellent diastereo- and enantioselectivity.

Abstract:

A catalytic (E)- to (Z)-isomerization of olefins using a photoredox catalyst under mild reaction conditions is presented. A variety of (Z)-alkenes can be prepared in the presence of visible light. A new reaction system allows an easy and efficient scale-up, as well as a continuous flow process in which the photocatalyst is immobilized in an ionic liquid and continuously recycled by simple phase separation.

Abstract:

The review highlights the different advantages associated with organocatalytic transformations performed in continuous-flow systems and presents the reactions which have been successfully achieved to date. Particular focus is placed on the comparison between batch and flow applications in order to show the advantages and disadvantages and to demonstrate the great potential for applying organocatalysis as well as combined organo and photoredox catalyzed reactions in continuous flow.

Abstract:

The first asymmetric metal-catalyzed Nazarov cyclization of N-heterocycles has been developed. The use of a chiral catalyst allows the enantioselective electrocyclization of N-heterocycles under mild conditions and the corresponding products are obtained in good yields with excellent enantio- and diastereoselectivity. The reaction mechanism and the absolute configuration of the obtained products are explained by means of computational studies.

Abstract:

A combination of ruthenium and photoredox catalysis allowed the ortho olefination of phenols. Using visible light, the direct CH functionalization of o-(2-pyridyl)phenols occurred, and diverse phenol ethers were obtained in good yields. The regeneration of the ruthenium catalyst was accomplished by a photoredox-catalyzed oxidative process.

Abstract:

The functionalization of CAr–SMe and Csp3–SMe bonds by direct exchange of the sulfur atom with an activated sp3-carbon has been developed. Reactions with LiCH2SiMe3 in the presence of a Nickel catalyst proceed with good yields and allow the conversion of aryl and benzyl methyl sulfides to trimethylsilylated products which are valuable precursors for the synthesis of olefins, various alcohols and amines, diols and aromatic carboxylic acids.

Abstract:

A dual catalytic system consisting of indium triflate and a chiral imidazolidinone catalyzes the asymmetric addition of aldehydes to N-acyl quinoliniums furnishing optically active dihydroquinolines in good yields and excellent selectivities. The products were further functionalized into optically active tetrahydroquinolines, quinolines and 6-oxa-2-aza-bicyclo[3.3.1]nonanes.

Abstract:

The aerobic, room-temperature coupling of tetramethylammonium trifluoromethylselenate with readily available boronic acids, boronic esters, and terminal alkynes has been developed. The method permits direct access to valuable trifluoromethylselenoarenes and alkynes under mild conditions. A convenient one-pot reaction, a scale up procedure as well as an extension to perfluoroalkylselenates are also presented to further demonstrate the synthetic utility of this reaction.

Abstract:

A protocol for the coupling of 3-iodoazetidines with Grignard reagents in the presence of an iron catalyst has been developed. A variety of aryl, heteroaryl, vinyl and alkyl Grignards were shown to participate in the coupling process to give the products in good to excellent yields. Furthermore, a short formal synthesis towards a pharmacologically active molecule was shown.

Abstract:

The application of cyclic and acyclic enol ethers as electrophiles in cross coupling reactions offers new possibilities for the preparation of functional compounds. A novel nickel catalyzed dealkoxylative cross coupling reaction allows access to structurally diverse allylsilanes and alcohol derivatives with high stereospecificity and in good yields under mild reaction conditions directly from the corresponding enol ethers.