An ew redox-active N-heterocyclic carbene (NHC) architecture is obtained using N-methylated pyrazinediimine iron complexes as precursors.The new species exhibit strong paccepting/s-donating properties and are able to ligate two metal centres simultaneously.T he redox activity was demonstrated by the reversible chemicalo xidation of ah eterobimetallic Fe 0 /Rh I example,w hich affords an isolable ligand-based radical cation. The reversible redox process was then applied in the catalytic hydrosilylation of 4,4'-difluorobenzophenone, where the reaction rate could be reversibly controlled as af unction of the catalyst oxidation state.T he new NHC exhibits high electrophilicity and nucleophilicity,w hich was demonstrated in the reversible activation of alcohols and amines.The electronic structure of the resulting complexes was investigated through various spectroscopic and computational methods.

We report an asymmetric bioinspired total synthesis of the fungal metabolites emeriones A–C via stereoselective late-stage epoxidation or endoperoxidation of two bicyclo[4.2.0]octadiene diastereomers. The central bicyclic scaffold is synthesized in an 8pi/6pi electrocyclization cascade of a stereodefined (E,E,Z,Z,E)-pentaene, which contains the fully assembled and unprotected side chains of the natural products. The pentaene is constructed convergently through Stille cross-coupling of two similarly complex polyenes. The anti-aldol side chain of the emeriones is made using a Paterson-aldol approach, and the epoxide of the dioxobicyclo[3.1.0] side chain is synthesized via an unusual ring-closure onto an oxidized para-methoxyphenyl acetal. Our total synthesis has enabled the revision of the structure of emerione C and the synthesis of a “missing” family member, which we hereby call emerione D.

We report asymmetric bioinspired total syntheses of the fungal metabolites emeriones A-C via stereoselective oxidations of two bicyclo[4.2.0]octadiene diastereomers. The central bicyclic scaffolds are prepared in an 8π/6π electrocyclization cascade of a stereodefined pentaene, which contains the fully assembled side chains of the emeriones. The anti-aldol side chain is made using a Paterson-aldol addition, and the epoxide of the dioxabicyclo[3.1.0]hexane side chain via ring-closure onto an oxidized acetal. Our work has enabled the structural revision of emerione C, and resulted in the synthesis of a "missing" family member, which we call emerione D. DFT calculations identified two methyl groups that govern torquoselectivity in the 8π/6π cascade.Natural products derived from polyenes that undergo cyclization/isomerization cascades initiated by an 8π electrocyclization have intrigued chemists for decades. [1] The emeriones (Figure 1), one such family of natural products that were isolated from the fungus E. nidulans, [2] display oxidized bicyclo[4.2.0]octadiene cores (red) flanked by a seven carbon aldol fragment (blue) and a propenyl-substituted dioxabicyclo[3.1.0]hexane system (black). The two side chains (blue and black) of emerione A (1) and B (2) share the same absolute configurations, while the bicyclo-[4.2.0]octadieneoxide central scaffolds are enantiomeric with respect to each other. Emerione C has a bridging endoperoxide on the central core, and its proposed structure has a stereochemical configuration similar to emerione B.Related substances like shimalactone A (3) [1p] and ocellapyrone B (4) [1m, n] have been synthesized, but the emeriones are arguably the most complex examples of such natural products, each containing twelve stereocenters, eight of which are contiguous, and two quaternary. Moreover, the dioxabicyclo[3.1.0]hexane system, also found in natural products like verrucosidin (5), [3] is a considerable synthetic challenge alongside the oxidized bicyclo[4.2.0]octadiene scaffolds. Emerione A inhibits NO production in lipopolysaccharide-induced RAW264.7 cells [2] as well as NDM-1 [4] at low micromolar concentrations, but the emeriones appear not to have been tested in other assays. Motivated both by their striking structures and potentially undiscovered bioactivities, we chose to target the emeriones for synthesis. We describe herein the successful completion of the syntheses, the structural revision of emerione C, and the synthesis of the originally proposed structure of emerione C, which we name emerione D.

Ein neuartiger Vertreter der N-heterocyclischen Carbene (NHC) konnte ausgehend von einem N-methylierten Pyrazindiimin-Eisenkomplex dargestellt werden. Dieser zeichnet sich durchseine Fähigkeit als starker p-Akzeptor/s-Donor aus und ermçglicht die gleichzeitige Koordination zweier Metallzentren. Die Redoxaktivitätd es Systems konnte durch reversible chemische Oxidation einer heterobimetallischen Fe 0 / Rh I-Komplexverbindung gezeigt und das dabei entstehende ligandenzentrierte Radikalkation isoliert werden. In einem ersten Beispiel konnte dieser reversible Redoxprozess in der katalytischen Hydrosilylierung von 4,4'-Difluorobenzophenon angewandt werden. Hierbei konnte die Reaktionsgeschwindigkeit durch den Oxidationszustand des Katalysatorsystems reversibel moduliert werden. Das neue NHC agiert sowohl als starkes Elektrophil als auchals Nukleophil, was durchdie reversible Aktivierung von Alkoholen und Aminen gezeigt werden konnte.D ie elektronische Struktur der resultierenden Komplexew urdem ittels verschiedener spektroskopischer als auchquantenchemischer Methoden untersucht.

We report an asymmetric bioinspired total synthesis of the fungal metabolites emeriones A–C via stereoselective late-stage epoxidation or endoperoxidation of two bicyclo[4.2.0]octadiene diastereomers. The central bicyclic scaffold is synthesized in an 8pi/6pi electrocyclization cascade of a stereodefined (E,E,Z,Z,E)-pentaene, which contains the fully assembled and unprotected side chains of the natural products. The pentaene is constructed convergently through Stille cross-coupling of two similarly complex polyenes. The anti-aldol side chain of the emeriones is made using a Paterson-aldol approach, and the epoxide of the dioxobicyclo[3.1.0] side chain is synthesized via ring-closure onto an oxidized para-methoxyphenyl acetal. Our total synthesis has enabled the revision of the structure of emerione C and the synthesis of a “missing” family member, which we hereby call emerione D. DFT calculations indicate the two methyl groups that reside on the cyclobutene ring are critical for the stereochemical outcome of 8pi/6pi electrocyclization.