Tris-ACE-(6,6′-bipyridyl)-α-cyclodextrin: synthesis and chirality of the tripodal metal complexes

This Letter describes the synthesis of a C₃-symmetrical tris-^ACE-(6,6′-bipyridyl)-α-CyD via ‘one-pot’ Staudinger-Aza-Wittig reaction (SAW). Metal complexation behavior was investigated by UV–vis and Circular Dichroism. Coordination of 6,6′-bipyridyl units with Cu^II and Ni^II cations, spontaneously generates a strong exciton coupling-type positive Cotton effect proving the formation of a Λ-helix with a left-handed screw propeller (M).     

A two-step valence tautomeric transition in a dinuclear cobalt complex

A dinuclear cobalt complex with cobalt centers bridged by a bis(dioxolene) ligand exhibits a rare two-step valence tautomeric transition.     

Efficient microwave syntheses of the compounds Os3(CO)11L, L = NCMe, py, PPh3

The results of simple microwave-assisted ligand substitution reactions of Os₃(CO)₁₂ are reported. In a remarkably short period of time, the labile complex Os₃(CO)₁₁(NCMe) is prepared in high yield without the need for a decarbonylation reagent such as trimethylamine oxide. Microwave irradiation of Os₃(CO)₁₂ in a relatively small amount of acetonitrile is shown to be a useful first step in two-step, one-pot syntheses of the cluster complexes Os₃(CO)₁₁(py) and Os₃(CO)₁₁(PPh₃).     

Fluorine-induced diastereodivergence discovered in an equally rare enantioselective syn-aza-Henry reaction

Attention to the aza-Henry reaction, particularly over the past two decades, has resulted in a wide range of effective catalysts for the enantio- and diastereoselective versions, driven by the versatility of the β-amino nitroalkane products as precursors to secondary amines and vic-diamines. Despite this broad effort, syn-diastereoselective variants are exceedingly rare. We have discovered a subset of α-fluoro nitroalkane additions that are characterized by an unusual crossover in diastereoselection, often delivering the products with high selectivities. We report here a rigorous comparative analysis of non-fluorinated and α-fluoro nitroalkanes in their additions to azomethines. Both homogeneous and heterogeneous catalysis were applied to probe the possibility that this phenomenon might be more widely operative in the enantioselective additions of fluorine-substituted carbon nucleophiles. A complete correlation within four categories is described that uncovered a clear trend, while revealing a dramatic and distinct reversal of diastereoselection that would normally go undetected.

A comparison of enantioselective aza-Henry reactions with both non-fluorinated and α-fluoro nitroalkanes reveals an unusual reversal of diastereoselection favoring the rare syn-aza-Henry product as a result of fluorine-based diastereodivergence.     

New Prospects toward the Synthesis of Difluoromethylated Phosphate Mimics

The difluoromethyl phosphonate motif plays a crucial role in the development of bioactive molecules as it is considered as a phosphate bioisoster. Since 2010, a renewal of interest to enlarge the panel of reactions to access these difluoromethylated phosphonate‐containing molecules has been witnessed. This Concept article charts the recent progress that has been made.     

Kinetic Resolution in the [2+2] Cycloaddition of Ketenes: An Experimental and Theoretical Study

The kinetic resolution of Z and E olefins by [2+2] cycloaddition with ketenes allows the isolation of pure E olefin, as well as the synthesis of pure cis‐cyclobutanones, starting from Z/E mixtures. A computational rationale for this kinetic difference is reported. The obtained difference of energy of activation matches with the experimental results.     

Hémisynthèse d''un nouvel isomère de la vinblastine

The reaction of the chloroindolenine of secopandoline $\text{2}$ with vindoline in acidic medium gives an isomer of the antitumor vinblastine $\text{1}$. This new compound is 14′-epi-20′-epivinblastine $\text{7}$.     

Die Struktur des Bisindolalkaloides Amatain ( = Grandifolin,Subsessilin)

The structure of the bisindole alkaloid amataine (= grandifoline, subsessiline) Amataine ( 1 ) was isolated from the roots of Hedranthera barteri (HOOK . F .) PICHON (Apocynaceae). In comparison to the alkaloid vobtusine ( 5 ), which was isolated from the same plant, 1 contains two hydrogen atoms less. By reduction of 1 with H₂/PtO₂ or with NaBH₄ dihydromataine ( = isovobtusine, 13 ) was formed which is isomeric to 5 . Acid catalysed water addition to 1 afforded hydratoamataine ( 15 ), which was reduced to 5 with NaBH₄. Thermolysis of 15 gave 1 . The difference between the two isomeric bases 5 and 13 has to be attributed to a different configuration at the spirocenter C(7). In contrast to 5 amataine ( 1 ) contains an ether bridge instead of a hydroxy group; this bridge is located between C (2′) and C (8).