Search results for " Force"

Pyrene-benzoylthiophene exciplexes as selective catalysts for the [2+2] cycloaddition between cyclohexadiene and styrenes.

2007

Efficient intramolecular fluorescence quenching in pyrene−benzoylthiophene systems leads to formation of exciplexes. These species interact with 1,3-cyclohexadiene (or styrenes), leading to reactive excited triplexes. The overall process affords [2+2] cross-cycloadducts with an average yield of 57%.

Die kristallstruktur von oligo[(2-hydroxy-1,3-phenylen)methylen]en

1984

The crystal structure of three tetranuclear phenolic compounds – 6,6′-bis (2-hydroxy-5-methylbenzyl)-4,4′-dimethyl-2,2′-methylenediphenol (1), 6-(2-hydroxy-3,5-dimethylbenzyl)-6′-(2-hydroxy-5-methylbenzyl)-4,4′-dimethyl-2,2′-methylendiphenol (2), and 6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-6′-(2-hydroxy-5-methylbenzyl)-4,4′-dimethyl-2,2′-methylene-diphenol (3) –, was determined by single crystal X-ray analysis. Intramolecular hydrogen bonds between all hydroxyl groups of adjacent phenolic units are found for all molecules. They are directed to the opposite end of the molecule by the ortho-methyl or ortho-tert-butyl group in compounds 2 and 3, while no special orientation is found in 1. Th…

4-Bromophenyl 2,3,4,5,6-pentabromophenyl ether

2002

The title compound, C12H4Br6O, belongs to a group of flame retardants known as polybrominated di­phenyl ethers (PBDE). Intermolecular Br⋯Br contacts in the bc plane give a sheet-like character to the structure of the title compound.

ChemInform Abstract: Polycondensed Nitrogen Heterocycles. Part 23. Pyrrolo(3,2-c)cinnolines by a Japp-Klingemann-Type Reaction.

1990

Pyrrolo[3,2-c]cinnoline derivatives were obtained by an unusual Japp-Klingemann reaction involving an intramolecular azadehalogenation on the pyrrole nucleus. Such an azadehalogenation represents the first example of Japp-Klingemann reaction in which the extrusion of positive chlorine ion is verified.

Excited states of [3.3](4,4')biphenylophane: the role of charge-transfer excitations in dimers with pi-pi interaction.

2010

The singlet and triplet electronic excitation manifold of [3.3](4,4')biphenylophane (BPP), an intramolecular dimer, and 4,4'-dimethylbiphenyl (DMBP), the corresponding monomer, has been analyzed by employing the approximate coupled-cluster singles and doubles model (CC2). The calculated triplet-triplet and singlet-singlet transient absorption spectra show good agreement with recent experimental results. The calculations suggest a strong interaction of the two biphenyl moieties of BPP in the first singlet and triplet excited states due to the overlapping pi-electron systems, and Forster-Dexter theory for weak coupling cannot be applied. Both the first excited singlet and triplet states of BP…

Enantioselective Synthesis of 2-Isoxazolines by a One-Flask Conjugate Addition/Oxime-Transfer Process

2009

Enantioselective isoxazoline synthesis: A combination of 1) a catalytic enantioselective conjugate addition of oximes to alpha,beta-unsaturated aldehydes and 2) an acid-catalyzed intramolecular oxime-transfer reaction lead to the first asymmetric synthesis of 3-unsubstituted 2-isoxazolines (see scheme).

ChemInform Abstract: Enantioselective Synthesis of 2-Isoxazolines by a One-Flask Conjugate Addition/Oxime-Transfer Process.

2009

Enantioselective isoxazoline synthesis: A combination of 1) a catalytic enantioselective conjugate addition of oximes to alpha,beta-unsaturated aldehydes and 2) an acid-catalyzed intramolecular oxime-transfer reaction lead to the first asymmetric synthesis of 3-unsubstituted 2-isoxazolines (see scheme).

ChemInform Abstract: Total Synthesis of (-)-Hymenosetin.

2016

Hymenosetin (I) and its N-methyl analogue are prepared in 11 and 8 steps, respectively, from citronellal employing an intramolecular Diels-Alder reaction as the key step.

1981

The proton spin-lattice relaxation time T1 was determined at 13,8, 55,2, and 90 MHz in polystyrene (PS-d0) and polystyrene deuterated at the chain (PS-d3) and the phenyl groups (PS-d5), respectively, at temperatures between −130 and +230°C. Furthermore, T1 was measured in isotopic mixtures of PS-d3 and fully deuterated PS-d8 where a separation into intramolecular and intermolecular contributions was possible through the deuteron dilution technique. Above 130°C, various distributions of correlation times provide a semiquantitative understanding of the different motins seen by the protons of the partially deuterated systems. Rotating frame relaxation times in PS-d3 and PS-d5 reveal librationa…

ChemInform Abstract: Reactivity and Selectivity of ortho-Metalated Rhodium(II) Complexes in C-H Insertion Reactions of α-Diazo Compounds.

2010

Regioselective intramolecular C−H insertion reactions of α-diazo β-keto esters and α-diazo ketones are mediated by Rh2[OOCR]4-x[PC]x (x = 1, 2; PC = ortho-metalated phosphine; R = CH3, C3F7). In particular, the intramolecular transformation of 1-diazo-5-methyl-3-propyl-2-hexanone catalyzed by Rh2[OOCCH3]2[PC]2 (PC = (C6H4)P(C6H5)2, head-to-tail (H−T) configuration) afforded only the tertiary C−H insertion product. By comparison, no C−H insertion reaction was promoted by doubly metalated complexes with a head-to-head (H−H) configuration. Rh2[OOCR]3[PC] compounds were found to be less suited for these type of reactions.