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498 results on '"RAABE, G."'

51. CYCLOADDITIONS .43. CYCLOBUTANONES VIA PHOTOREACTIONS OF CHROMIUM-CARBENE COMPLEXES WITH OLEFINS AND DIENES - A COMPARISON WITH THE TRADITIONAL KETENE METHOD

Author

KOBBING, S, Mattay, Jochen, and RAABE, G

Subjects
2+2, CYCLOBUTANONES, CYCLOADDITIONS, KETENES, CHROMIUM-CARBENE COMPLEXES
Abstract

Photolysis of chromium-carbene complexes 1 in the presence of olefins and dienes yields cyclobutanones 4 and 5 with varying stereoselectivity. Under oxidative conditions lactones 6, 7, 8, and 10 are obtained as byproducts. Thermal reactions of ketenes 3 with olefins and dienes yield the same cyclobutanones with usually equal selectivities. In the case of 2,3-dihydro-1,4-dioxin as olefin, diene 9 is obtained as a byproduct. Cycloaddition reactions of 1a or 3a with 1,2-dimethylenecyclopentane (11) yield the spirocyclic cyclobutanones 12 and 13. The symmetric ketone 16 and the ketene dimer 17 are formed as additional products upon cycloaddition of ketene 3b to tetraethoxyethylene. Novel alpha-(butylthio)cyclobutanones 4j, k, l, m and 5k, l are formed by cycloaddition reactions of the newly prepared compounds 1c and 3c. The ketene dimer 20 is formed by thermal reactions of 3a with olefins. Unusually low stereoselectivities are observed in the case of photolytic reactions of 1c with dienes.

Published
1993

62. Laboratory studies of atmospheric aqueous phase free radical chemistry: Kinetic and spectroscopic laboratory studies of reactions of NO3 and SO4- radicals with aromatic compounds

Author

Herrmann, H., Exner, M., Jacobi, Hans-Werner, Raabe, G., Reese, A., Zellner, R., Herrmann, H., Exner, M., Jacobi, Hans-Werner, Raabe, G., Reese, A., and Zellner, R.

Abstract

Recent results from kinetic and spectroscopic laboratory studies of reactions of free radicals such as NO3 and SO4- with aromaticcompounds in aqueous solution at T = 298 K are presented. Three different experimental approaches, (i) laser photolysis-visible long-pathlaser absorption, (ii) laser photolysis-UV long-path laser absorption and (iii) time-resolved broadband diode-array spectroscopy, havebeen used to investigate the kinetics of reactions of NO3 and SO4- with aromatics, as well as the formation of oxidation intermediates.For the reactions of NO3 with benzene (1), anisole (2), p-xylene (3), p-cresol (4), toluene (5), mesitylene (6) and 1,4-dimethoxybenzene(7), rate coefficients of k(1) = (4.0 +/- 0.6) x 10(8) 1 mol(-1) s(-1), k(2) = (1.0 +/- 0.4) x 10(9) 1 mol(-1) s(-1), k(3) (1.6 +/- 0.1) x10(9) 1 mol s(-1), k(2) = (1.0 +/- 0.4) x 10(9) mol(-1) 1 s(-1), k(3) = (1.6 +/- 0.1) x 10(9) 1 mol(-1) s(-1), k(4) = (8.4 +/- 2.3) x 10(8)1 mol s(-1) k(5) = (1.2 +/- 0.3) x 10(9) 1 mol(-1) s(-1), k(6) = (1.3 +/- 0.3) x 10(9) 1 mol(-1) s(-1) and k(7) = (1.0 +/- 0.3) x 10(9) 1mol(-1) s(-1) were obtained. For the corresponding reactions of SO4- with benzene (8), toluene (9), p-xylene (10), p-cresol (11) andmesitylene (12), rate coefficients of k(8) = (6.4 +/- 2.5) x 10(8) 1 mol(-1) s(-1), k(9) = (1.3 +/- 0.6) x 10(9) 1 mol(-1) s(-1), k(10) =(2.7 +/- 0.9) x 10(9) 1 mol(-1) s(-1)k(11) = (2.8 +/- 0.8) x 10(9) 1 mol(-1) s(-1) and k(12) = (1.3 +/- 0.4) x 10(9) 1 mol(-1) s(-1) weredetermined. Reactivity correlations for both radical species with the aromatic compounds are presented and potential applications of suchcorrelations are discussed. In addition, the effect of ionic strength in the reactions of NO3 with benzene and toluene has been investigated.Transient intermediates have been spectroscopically identified in the reactions of the sulfate radical anion in aerated as well as inoxygen-free solutions. The nature of these intermediates is discussed in view of the existing lite

Published
1995

70. ChemInform Abstract: Formal Asymmetric Synthesis of Pentalenolactone E and Pentalenolactone F. Part 1. Retrosynthesis and π‐Facial Differentiation in Palladium‐Catalyzed and Dipolar [3 + 2]‐Cycloaddition Reactions of Bicyclic Alkenes: Evidence for Electrostatic Control of Stereoselectivity.

Author

ROSENSTOCK, B., primary, GAIS, H.‐J., additional, HERRMANN, E., additional, RAABE, G., additional, BINGER, P., additional, FREUND, A., additional, WEDEMANN, P., additional, KRUEGER, C., additional, and LINDNER, H. J., additional

Published
1998
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74. Formal Asymmetric Synthesis of Pentalenolactone E and Pentalenolactone F-1. Retrosynthesis and π-Facial Differentiation in Palladium-Catalyzed and Dipolar [3 + 2]-Cycloaddition Reactions of Bicyclic Alkenes: Evidence for Electrostatic Control of Stereoselectivity

Author

Rosenstock, Bernd, primary, Gais, Hans-Joachim, additional, Herrmann, Eva, additional, Raabe, G., additional, Binger, Paul, additional, Freund, Andreas, additional, Wedemann, Petra, additional, Krüger, Carl, additional, and Lindner, Jörg, additional

Published
1998
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