Johannes Kaschel

anti-Oligoannelated THF Moieties: Synthesis via Push−Pull-Substituted Cyclopropanes‡

The first synthesis of anti-fused oligoannelated THF moieties is reported. The key transformation of the synthetic sequence, consisting of cyclopropanation, reduction and oxidation, is the expansion of a push-pull-substituted three-membered ring into a five-membered enol ether system. A repetition of the sequence allows the creation of oligoacetals up to a nonacyclic system.

Domino reactions of donor-acceptor-substituted cyclopropanes for the synthesis of 3,3'-linked oligopyrroles and pyrrolo[3,2-e]indoles.

Multiple displacement of oxygen: Electron-rich oligopyrroles and pyrrolo[3,2-e]indoles are generated by a domino process induced by donor-acceptor-substituted cyclopropanes. Up to seven molecules of water are eliminated, thus allowing the introduction of nitrogen and aromaticity.

From furan to molecular stairs: syntheses, structural properties, and theoretical investigations of oligocyclic oligoacetals.

The synthesis of oligocyclic oligoacetals using five-membered rings as repetitive unit is described. Furan was used as the starting material, which is converted by a three-step procedure consisting of twofold cyclopropanation, reduction, and oxidative ring enlargement into a tricyclic bis(enol ether). A repetition of this synthetic procedure leads to the formation of extended oligoacetal systems. Insights into the structures were gained by X-ray crystallographic investigations and revealed helical arrangements of the subunits in the solid-state. DFT (B3LYP) calculations have been carried out to elucidate the transition state of the ring enlargement and the flexibility of the annelated oligocyclic systems. Strain energies and topologies of potential cyclically condensed oligoacetals are predicted.

Donor-substituted nitrocyclopropanes: immediate ring-enlargement to cyclic nitronates.

The reaction of donor-substituted alkenes with α-diazo-α-nitro ethyl acetate under Rh catalysis was investigated; respective nitrocyclopropanes with a geminal ester functionality were generated in situ. Strong electron donors immediately led to ring-enlargement. In all cases, the nitro group was inserted forming cyclic nitronates whereas the ester moiety was not incorporated into the ring system. DFT studies revealed that the formation of cyclic nitronates is kinetically as well as thermodynamically favored over the formation of cyclic ketene acetals.

One Pot, Two Phases: Iron-Catalyzed Cyclopropanation with In Situ Generated Diazomethane†

Tamed! The safe handling of diazomethane can be accomplished by a two-phase reaction. After being generated in aqueous media, the highly reactive species transfers to the organic phase and directly converts alkenes into cyclopropanes (see scheme). An air-stable iron(III) porphyrin complex serves as the catalyst.

CCDC 849623: Experimental Crystal Structure Determination

Related Article: Johannes Kaschel,Tobias F. Schneider,Daniel Kratzert,Dietmar Stalke,Daniel B. Werz|2013|Org.Biomol.Chem.|11|3494|doi:10.1039/c3ob40228b