Gold-Catalyzed Cyclisation by 1,4-Dioxidation.

Amide-substituted diynes were cyclized in the presence of a cationic gold catalyst and an external nucleophile leading to 1-indenones and 1-iminoindenones. The electron-donating features of the nitrogen atom enable the formation of a reactive ketene iminium ion, which can be trapped by either diphenyl sulfoxide or anthranil as nucleophiles in a subsequent oxidation step, providing substituted inden-1-on-3-carboxamides.

Dual gold-catalyzed head-to-tail coupling of iodoalkynes.

Various haloalkynes are converted in the presence of a dual activation gold catalyst. Via a dual activation process a completely atom economic head-to-tail coupling delivers gem-dihalogenated conjugated enynes as valuable building blocks for organic synthesis.

Are ß-H eliminations or alkene insertions feasible elementary steps in catalytic cycles involving gold(I) alkyl species or gold(I) hydrides?

The ß-H-elimination in the (iPr)AuEt complex and its microscopic reverse, the insertion of ethene into (iPr)AuH, were investigated in a combined experimental and computational study. Our DFT-D3 calculations predict free-energy barriers of 49.7 and 36.4 kcal mol(-1) for the elimination and insertion process, respectively, which permit an estimation of the rate constants for these reactions according to classical transition-state theory. The elimination/insertion pathway is found to involve a high-energy ethene hydride species and is not significantly affected by continuum solvent effects. The high barriers found in the theoretical study were then confirmed experimentally by measuring decomposition temperatures for several different (iPr)Au(I) -alkyl complexes which, with a slow decomposition at 180 °C, are significantly higher than those of other transition-metal alkyl complexes. In addition, at the same temperature, the decomposition of (iPr)AuPh and (iPr)AuMe, both of which cannot undergo ß-H-elimination, indicates that the pathway for the observed decomposition at 180 °C is not a ß-H-elimination. According to the calculations, the latter should not occur at temperatures below 200 °C. The microscopic reverse of the ß-H-elimination, the insertion of ethene into the (iPr)AuH could neither be observed at pressures up to 8 bar at RT nor at 1 bar at 80 °C. The same is true for the strain-activated norbornene.

Synthesis and evaluation of a netropsin-proximicin-hybrid library for DNA binding and cytotoxicity.

The proximicins A-C (1-3) are novel naturally occurring gamma-peptides with a hitherto unknown 2,4-disubstituted furan amino acid as a core structure. They show a moderate cytotoxic activity and induce upregulation of cell cycle regulating proteins (p53 and p21) and lead to cell cycle arrest in G0/G1-phase. Hybrid molecules combining structural motifs of the proximicins and of netropsin (4), a structurally related natural product, seem to have similar effects. Herein we describe the synthesis of a netropsin-proximicin-hybrid library and its evaluation regarding cytotoxicity and minor groove binding activity.