Derivatives of pyrido[2,3‐b][1,4]diazepine and of the dipyrido[1,2‐a:2′,3′‐b]imidazole heterocyclic system

With a continuing interest in heteropolycyclic systems which may show biological activities, we studied the reaction of 3‐amino‐2‐(methylamino)pyridine with diethyl 1,3‐acetonedicarboxylate in order to develop pyridodiazepinone derivatives. From the reaction mixture, we separated dipyrido[1,2‐a:2′,3′‐d]imidazole derivatives ( 3 and 4 ) besides two isomeric pyrido[2,3‐b][1,4]diazepine derivatives ( 5 and 6 ) in which the complex structural differentiation was achieved through nmr experiments and chemical evidence. Several attempts to elaborate isomers 5 and 6 have not yet given significant results.     

Polycyclic Indoline‐Benzodiazepines through Electrophilic Additions of α‐Imino Carbenes to Tröger Bases

Polycyclic indoline‐benzodiazepines can be accessed through the intermolecular reaction of Tröger bases with N‐sulfonyl‐1,2,3‐triazoles. Under Rh^II catalysis, α‐imino carbenes are generated and a subsequent cascade of [1,2]‐Stevens, Friedel–Crafts, Grob, and aminal formation reactions yield the polycyclic heterocycles as single isomers (d.r.>49:1, four stereocenters including two bridgehead N atoms). Further ring expansion by insertion of a second α‐imino carbene leads to elaborated polycyclic 9‐membered‐ring triazonanes.     

RAFT Polymerization in Bulk and Emulsion

Detailed models of the RAFT polymerization in both non-segregated (bulk) and segregated (seeded emulsion) systems are presented. It is shown that satisfactory agreements between experiments and models can be achieved, and that effects such as inhibition and retardation, or the polymerization behavior at high conversions can be readily explained. In all cases the model parameter fitting has been minimized, being mostly limited to the rate coefficients of the addition/fragmentation reactions in the RAFT polymerization. Therefore, such models are believed to be invaluable tools towards a deeper understanding of the main phenomena underlying RAFT polymerization.     

A fast contraction mapping for solving multibody systems

The simulation of complex multibody systems with contacts and friction requires a fast and robust solver for complementarity problems. This work presents an efficient method which can solve large cone-complementarity problems by means of a fixed point iteration. Our method performs like a contractive mapping, providing a monotonic approximation to the exact solution. The algorithm features high computational performance even if thousands of unilateral constraints are added to the system. Also, this scheme fits well in a real-time simulation context because it can be terminated prematurely. As a benchmark for testing the method in challenging situations, we propose the simulation of the granular flow in a fourth-generation bebble-bed nuclear reactor, including 150'000 rigid bodies and more than a million of constraint multipliers. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A(SLq(2)) at Roots of Unity is a Free Module over A(SL(2))

It is shown that when q is a primitive root of unity of order not equal to 2 mod 4, A(SL_q(2)) is a free module of finite rank over the coordinate ring of the classical group SL(2). An explicit set of generators is provided.     

Studying Natural Buckyballs and Buckybowls in Fossil Materials

Buckyballs (fullerenes) were first reported over 30 years ago, but still little is known regarding their natural occurrence, since they have so far only been found at sites of high‐energy incidents, such as lightning strikes or meteor impacts, but have not been reported in low‐energy materials like fossil fuels. Using ultrahigh‐resolution mass spectrometry, a wide range of fullerenes from C₃₀ to C₁₁₄ was detected in the asphaltene fraction of a heavy crude oil, together with their building blocks of C_10nH₁₀ stoichiometry. High‐level DLPNO‐CCSD(T) calculations corroborate their stability as spherical and hemispherical species. Interestingly, the maximum intensity of the fullerenes was found at C₄₀ instead of the major fullerene C₆₀. Hence, experimental evidence supported by calculations show the existence of not only buckyballs but also buckybowls as 3‐dimensional polyaromatic compounds in fossil materials.     

New chiral polyfunctional cyclobutane derivatives from (−)-verbenone: possible surfactant behaviour

New enantiopure cyclobutane derivatives have been synthesized from a chiral precursor derived from (?)-verbenone. The cyclobutane moiety acts as a chiral platform to afford a γ-amino acid function in a branched side-chain containing an additional stereogenic centre as well as additional C₆ or C₁₆-alkyl chains linked to the ring by means of an amine or an amide function. One of these compounds, obtained as a 1:2 mixture with its TFA salt has been investigated, suggesting behaviour as a good surfactant and its critical micellar concentration has been determined.