High regio-, chemo-, and stereoselectivity via low-temperature 4 + 3 cycloadditions. Convergent synthesis of multifunctionalized vinylmetals (M = Si, Sn) and S-vinyl benzenecarbothioates

A series of enantiomerically pure 8-oxabicyclo[3.2.1]oct-6-en-3-ones functionalized in the unsaturated two-carbon bridge has been prepared by the title reaction. Carbocation reactivity has been fined-tuned at -95 degrees C and adjusted to diene nucleophilicity. Conventional electrophilic substitution of 3-silylated and 3-stannylated furan is suppressed in favor of the rapid 4 + 3 cycloaddition mode. In the case of cycloadduct 13A, stereoselectivity (17:1) is perfectly matched to regioselectivity (17:1). High stereoselection as well as unprecedented regioselection and chemoselection is attributed to the low-temperature cycloaddition protocol and the design of chiral auxiliary and tether.     

Gezielte Synthese von Kohlenwasserstoff-verbrückten Komplexen. Nucleophile addition von Pentacarbonylrhenat und -manganat an π-gebundene Dien-, Cyclodien-, Trimethylenmethan-, Cycloheptatrienyl- und Alkin-Liganden

Pentacarbonyl-rhenate and -manganate react with the cationic complexes [cpMo(CO)₂(diene)]⁺, [cpMo(CO)₂(cyclopentadiene]⁺, [cpMo(CO)₂(cyclohexadiene)]⁺, [cpMo(CO)₂(trimethylenemethane]⁺, [(OC)₃Mo(η⁷-C₇H₇)]⁺, [cp(OC)-(Ph₃P)Mo(alkyne)]⁺ to give the corresponding heteronuclear hydrocarbon-bridged complexes.     

Übergangsmetallkomplexe mit Anionen von 1-substituierten 1,2,3,4-Tetrazolin-5-onen und -thionen und von 1,3-Thiazolin-2-thion

Transition Metal Complexes with Anions of 1-substituted Tetrazolinones and -thiones and of 1,3-Thiazolin-2-thione The preparation of a series of anionic and phosphine containing complexes with the ambivalent anions of 1-R-tetrazolin-5-ones and -5-thiones, and of 1,3-thiazolin-2-thione is reported. According to the i.r. and ¹H n.m.r. spectra the S-heterocycles are bonded through the exocyclic sulfur atom to the metal; in the oxotetrazolinate compounds coordination occurs via the N² or N⁴ ring atoms. The copper and silver complexes [(Ph₃P)MX]₂ (X = anionic heterocycle) have been found to be dimeric.     

Cover Picture

The cover picture shows a model of the "progenitor-TADDOLs" in front of a panorama of the Fünffingersstocks and the Wenden Glacier in the Titlisgebiet (Switzerland). The model is flanked by a stylized view of the general mechanistic model for the preferred stereochemical pathway of the Ti-TADDOLate-catalyzed reaction of chelating substrates (left) and a blackboard (right) showing formulae of compounds that can be prepared with high enantioselectivity by nucleophilic addition in the presence of titanium TADDOLates. From TADDOL, introduced in 1982, a genuine auxiliary system for the "introduction of chirality" (not only by reaction) has been developed, which, in the final sprint against the competition has a good chance of securing a place on the winning podium. The photograph of the mountain landscape was taken by Dr. J. Frackenpohl, the cover picture was generated by one of the authors (A.H.) of the comprehensive review of TADDOLs in this issue (p. 92 ff.) with the help of the program Povray. Supporting information for this article is available on the WWW under http://www.angewandte.com or from the author.     

A mass spectrometric investigation of non-covalent interactions between ruthenium complexes and DNA

Electrospray ionisation mass spectrometry was used to investigate reactions between six ruthenium compounds and three different non self-complementary duplex oligonucleotides containing 16 base pairs. Each of the compounds studied formed non-covalent complexes containing between one and five ruthenium molecules bound to DNA. Competition experiments involving duplex 16mers and pairs of ruthenium compounds were used to determine the order of relative binding affinities of the metal compounds. Other competition experiments involving ruthenium compounds, and the organic DNA binding agents daunomycin and distamycin, provided information about the sites and modes of DNA binding of the ruthenium compounds.     

An Accelerated Coordinate Gradient Descent Algorithm for Non-separable Composite Optimization

Journal of Optimization Theory and Applications - Coordinate descent algorithms are popular in machine learning and large-scale data analysis problems due to their low computational cost iterative...     

High-spin 52 117 Te: Rotational bands? Noncollective oblate

¹¹⁷Te has been studied via⁸²Se(⁴⁰Ar,5n)¹¹⁷Te, and a new, substantially extended level scheme is proposed to I53/2. Our TRS calculations suggest rotational bands, but with an experimental sensitivity of 2%, we see none. Our results differ from those of Sharma, et al, who report two isolated E2 bands. We find them less band-like, being joined at the top and changed in content and order. We suggest a noncollective oblate shape for a new 39/2^– level.This work is supported in part by the Department of Energy under Contract No.DE-AC03-76SF0098(LBL).