W Tungsten

Enantiopure alleno–acetylenic macrocycles have been prepared and fully characterized. Their extraordinary intense circular dichrosim (see picture) has been extensively studied and a mechanism for this remarkable response has been proposed. Additionally, the extent of the aromaticity was investigated by using the electron localization function. For more details see the Full Paper by F. Diederich, H. S. Rzepa et al. on page 9796 ff.

Metal–Organic Framework (MOF) materials containing either Cu or Au centers can act as catalysts for the cyclopropanation of alkenes with diazoacetates. In their Full Paper on on page 9789 ff., A. Corma et al. describe Cu and Au MOFs that are active and reusable heterogeneous catalysts for cycloproponation of alkenes with high chemo- and diastereoselectivities. This example is the first use of these materials to induce the carbene transfer reactions from diazo compounds.

The CO2 capture capacity, adsorption mechanism, and degradation characteristics of two sorbents, silica-supported tetraethylenepentamine (TEPA/SiO2) and polyethylene-glycol-modified TEPA/SiO2 (PEG/TEPA/SiO2), are studied by diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry. The CO2 capture capacities of TEPA/SiO2 and PEG/TEPA/SiO2 are determined to be 2087 and 1110 μmol CO2 g−1 sorbent, respectively. Both sorbents adsorb CO2 as hydrogen-bonding species, NH2O, and carbamate/carboxylate species. The CO2 adsorption half-time increases with the number of CO2 capture cycles. Infrared results suggest that the increased adsorption half-time is a result of diffusion limitation, caused by accumulation of TEPA and PEG species on the surface of the sorbent particles. The degradation of TEPA/SiO2 is found to correlate with the accumulation of carboxylate/carbamic species. The addition of PEG decreases the degradation rate of the sorbent and slows down the formation of carboxylate species. These carboxylate species can block CO2 capture on amine (NH2/NH) sites. The stabilizing role of PEG on TEPA/SiO2 can be attributed to hydrogen-bonding between TEPA (NH2/NH)and PEG (OH).The CO2capture capacity, adsorption mechanism, and degradation characteristics of two silica-supported tetraethylenepentamine sorbents, one of which is modified with polyethylene glycol (PEG), are studied. The addition of PEG slows down the rate of sorbent degradation by inhibiting the formation of a carboxylate species.

Saframycins, safracins, renieramycins, cribrostatins, and esteinascidins are 6,15-iminoisoquino[3,2-b]3-benzazocine compounds that constitute the largest subgroup among the antitumor antibiotics belonging to the tetrahydroisoquinoline family. Their structural complexity has led to widespread synthetic attention to obtain them in both racemic and enantiopure forms. Publication in 1996 of the first total synthesis of ecteinascidin 743 by Corey’s group was an important milestone, but the development of preparative protocols for these structures has continued, offering new possibilities to exploit the biological activity of the above-mentioned natural products and their analogues. This minireview is intended to update this progress following a methodological rather than a chronological organization. Besides of a brief description of the different strategies evolved from retrosynthetic analyses, which have been organized according to the order of bonding events that will link the precursors, semisynthetic approaches and a brief account of the total syntheses of ecteinascidin 743, have been analyzed.New perspectives: This minireview is intended to update the synthetic contributions to obtain saframycin analogues. These compounds constitute the largest subgroup among the tetrahydroisoquinoline antitumor antibiotics. A brief description of the different strategies has been organized according to the order of bonding events that will link the precursors (see scheme).

The copper-catalyzed conjugate addition of Grignard reagents to 3-substituted cyclic enones allows the formation of all-carbon chiral quaternary centers. We demonstrate in this article that N-heterocyclic carbenes act as efficient chiral ligands for this transformation. High enantioselectivities (up to 96 % ee) could be obtained for a variety of substrates.Asymmetric chemistry: The copper-catalyzed conjugate addition of Grignard reagents to 3-substituted cyclic enones allows the formation of all-carbon chiral quaternary centers (see scheme). N-Heterocyclic carbenes act as efficient chiral ligands for this transformation. High enantioselectivities (up to 96 % ee) could be obtained for a variety of substrates.

The zinc connection! Reaction of bulky alcohols with [Zn2Cp*2] in the presence of a Lewis base allowed the isolation of the first zinc–zinc bonded complexes containing a ZnO bond (see scheme).