Zum Mechanismus photochemisch ausgelöster radikalischer Cyclisierungen

Radical cyclizations of isoprenoid polyalkene-1,1-dicarbonitriles are efficiently initiated upon photoinduced electron transfer from the alkene to the electronically excited states of cyanoarenes or 2,4,6-triaryl pyrylium salts. In the course of these reactions, a radical cation, formed at the w?terminal site of the alkene is in situ trapped by anti-Markovnikow addition of a nucleophile. The radical thus formed initiates a sequence of 6?endo?trig and 5?exo?trig ring closures, resulting in a resonance-stabilized radical. Subsequent reduction to the corresponding carbanion, followed by protonation furnishes mono- and polycyclic products in good yields. The mechanism of these synthetically useful biomimetic cyclizations was supported using time-resolved UV-vis spectroscopy, conductivity and molecular modelling studies

Intramolecular [2+2] cycloaddition of some 1,n-diene-1,1-dicarbonitriles - Difference between singlet and triplet reactivity

Intramolecular [2+2] cycloadditions on direct irradiation have been observed with four 1-alkene-1,1-dicarbonitriles bearing an additional C=C bond positioned in Delta(5), Delta(6), or Delta(7) within a flexible chain. The cycloadducts formed are the "parallel" regioisomers. These cycloadditions occur by excitation of an intramolecular charge transfer complex formed by the two double bonds. Triplet sensitisation has also been investigated in one case and found also to lead to intramolecular [2 + 2] cycloaddition, however furnishing the "crossed" regioisomer. It appears that the triplet cycloaddition path, other than the singlet one, does not involve an exciplex but rather proceeds in two steps via the most stable triplet 1,4-diradical. (C) 2002 Elsevier Science B.V. All rights reserved

Biomimetic radical polycyclizations of isoprenoid polyalkenes initiated by photoinduced electron transfer

494-497Isoprenoid polyalkene radicals, formed by anti- Markovnikov addition of a nucleophile to their parent radical cations, which are readily accessible via photoinduced electron transfer, undergo cascade cyclizations. The regioselectivity is efficiently controlled by the substitution pattern, i.e., the generally observed 6-endo-trig mode is replaced by 5-exo-trig, if electron-deficient double bonds (e.g. 1, 1-dicyanovinyl groups) are involved. Moreover, remarkably high asymmetric inductions have been achieved by the use of chiral spirocyclic dioxinones, derived from the chiral auxiliary (-)-menthone, notably remotely located from the initiationsite ofthe cyclizations.These asymmetricphotoinduced cyclizations constitute strong evidence of spontaneous coiling/folding of the terpenoid polyalkene chain and give ready access to the enantiomerically pure tricyclic terpenoids of complementary chiralities by means of the single chiral auxiliary (-)-menthone

Grid Workflow Approach using the CELLmicrocosmos 2.2 MembraneEditor and UNICORE to commit and monitor GROMACS Jobs

Rubert S, Gamroth C, Krüger J, Sommer B. Grid Workflow Approach using the CELLmicrocosmos 2.2 MembraneEditor and UNICORE to commit and monitor GROMACS Jobs. In: Warzecha K-D, Packschies L, eds. CEUR Workshop Proceedings. Vol 826. CEUR-WS; 2012.Molecular dynamic simulations of membrane systems are an important method for the prediction and analysis of physicochemical properties. The CELLmicrocosmos 2.2 MembraneEditor (CmME) provides a comfortable workflow to generate lipid membranes with different conformations. While CmME is intended to generate molecular structures on desktop and mobile computers in a very short time, the atomic simulation of exported membranes needs external high performance computer resources. In this work, a first approach of a direct connection between CmME and a cluster running GROMACS using the Gridmiddleware UNICORE-6 is discussed