Very high-resolution photogrammetric and geodetic measurements about the deformation of transverse ridges on Murtèl, Muragl and Suvretta rock glaciers in the Swiss Alps are discussed. The ridges are advected downstreams with a speed that equals the overall speed of the creeping permafrost within the significance level of the applied techniques. Any process of ridge formation is, thus, overlain on the mass creep. In fact, measurements yield local speed maxima on top of the ridges that can be explained by differential movement due to ridge growth through bulging under compressive flow. This hypothesis is consistent with results from laboratory experiments that were performed on a model ramp employing mixtures of Xanthan Gum, sand and gravel. Indications were also found that overthrusting is involved in the development of transverse ridges on rock glaciers.The photogrammetric and geodetic measurements of this study were quantitatively analysed on the basis of mass conservation, which can be expressed by the kinematic boundary condition at the surface (Hutter, 380 A. Kääb and M. Weber

The continued development of transition-metal-mediated C-C bond activation/cleavage methods would provide even more opportunities to implement novel synthetic strategies. We have explored the Rh(I)-catalyzed C-C activation of cyclobutanols resident in hydroxylated derivatives of pinene, which proceed in a complementary manner to the C-C bond cleavage that we have observed with many traditional electrophilic reagents. Mechanistic and computational studies have provided insight into the role of C-H bond activation in the stereochemical outcome of the Rh-catalyzed C-C bond activation process. Using this new approach, functionalized cyclohexenones that form the cores of natural products, including the spiroindicumides and phomactin A, have been accessed.

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A possible biosynthetic link between atropurpuran, the hetidine diterpenoid alkaloids and the alkaloid arcutine and congeners is proposed. The feasibility of aspects of this biosynthesis, especially key 1,2-rearrangements, have been examined computationally.

An approach to construct enantiopure complex natural product-like frameworks, including the first reported synthesis of a C17 oxygenated taxoid scaffold, is presented. A palladium-catalyzed C-C activation/cross-coupling is utilized to access these structures in a short sequence from (+)-carvone; the scope of this reaction is explored.

Monomeric ferrocene bis-imidazoline bis-palladacycles (FBIP) have recently been reported to be efficient bimetallic catalysts in different sorts of asymmetric reactions by the cooperation of two Pd(II) centers. A crucial parameter regarding the efficiency of reactions catalyzed in a bimetallic mode isin generalthe intermetallic distance of both catalytically relevant metal centers. In this article we describe the structural elucidation of the monomeric FBIP catalyst type (usually generated in situ from a catalytically inactive dimeric chloride bridged precatalyst) by X-ray crystal structure analysis. Two dicationic monomeric complexes are compared to a neutral complex. The solid-state structures reveal varying Pd–Pd distances ranging from 3.15 to 5.27 Å for the doubly charged complexes, whereas for the neutral complex a distance of 3.28 Å has been found. This variability is supposed to be one of the key advantages of a ferrocene backbone in a bimetallic catalyst system, since the Fe–Cp bonds allow the bimetallic complex to readily open and close like a pair of scissors, employing just a few degrees of rotational freedom. In addition, on the basis of the nature of the reported catalyst species, we suggest that a permanent switch among neutral and mono- and dicationic catalyst species by a Brønsted acid such as acetic acid might facilitate different elementary steps in a catalytic cycle. By DFT calculations we have found that weak d8–d8 interactions contribute to short Pd–Pd distances but are less important than dispersive interactions, which can even overcome the Coulombic repulsion of two cationic palladium centers.

Arcutinidine and other arcutinidine-type diterpenoid alkaloids feature an intricate polycyclic, bridged framework with unusual connectivity. A chemical network analysis approach to the arcutane skeleton enabled the identification of highly simplifying retrosynthetic disconnections, which indicated that the caged structure could arise from a simpler fused ring system. On this basis, a total synthesis of arcutinidine is reported herein, featuring an unprecedented oxopyrrolium Diels− Alder cycloaddition which furnishes a key tetracyclic intermediate. In addition, the synthesis utilizes a diastereoselective oxidative dearomatization/cycloaddition sequence and a SmI 2 -mediated C−C coupling to forge the bridged framework of the natural products. This synthetic plan may also enable future investigations into the biosynthetic relationships between the arcutanes, the related diterpenoid atropurpuran, and other diterpenoid alkaloids.Communication pubs.acs.org/JACS

Spirocyclic azlactones are shown to be useful precursors of cyclic quaternary amino acids, such as the constrained cyclohexane analogues of phenylalanine. These compounds are of interest as building blocks for the synthesis of artificial peptide analogues with controlled folds in the peptide backbone. They were prepared in the present study by a step- and atom-economic catalytic asymmetric tandem approach, requiring two steps starting from N-benzoyl glycine and divinylketones. The key of this protocol is the enantioselective formation of the azlactone spirocycles, which involves a PdII-catalyzed double 1,4-addition of an in situ generated azlactone intermediate to the dienone (a formal [5+1] cycloaddition). As the catalyst, a planar chiral ferrocene bispalladacycle was used. Mechanistic studies suggest a monometallic reaction pathway. Although the diastereoselectivity was found to be moderate, the enantioselectivity is usually high for the formation of the azlactone spirocycles, which contain up to three contiguous stereocenters. Spectroscopic studies have shown that the spirocycles often prefer a twist over a chair conformation of the cyclohexanone moiety.