Comparison of syn dehydrohalogenations from -1-bromo-2-chlorocycloalkanes promoted by complex base and by potassium -butoxide
作者:Alan P. Croft、Richard A. Bartsch
DOI:10.1016/s0040-4039(00)88009-0
日期:1983.1
Compared with t-BuOK-t-BuOH, syn eliminations from trans-1-bromo-2-chlorocycloalkanes (C4-C8) induced by NaNH2-NaO-t-Bu in THF are rapid, exhibit greater propensity for dehydrechlorination and show little sensitivity to ring size of the dihalocycloalkane.
Kinetics of alkylhalocarbene rearrangements: modulation by fluorine substituents
作者:Robert A. Moss、Guo Jie Ho、Weiguo Liu
DOI:10.1021/ja00029a025
日期:1992.1
Rate constants were measured by laser flash photolytic methods for hydrogen and carbon 1,2-migrations in four different alkylchlorocarbenes and in the analogous alkylfluorocarbenes. The carbenes, products, and rate constants (s-1) were as follows: phenoxymethylchlorocarbene to (Z)- and (E)-1-chloro-2-phenoxyethene (Z/E approximately 4/1), k = 3.6 x 10(7); phenoxymethylfluorocarbene to (Z)-1-fluoro-2-phenoxyethene (Z/E > 10/1), k = 1.3 x 10(7); neopentylchlorocarbene to (Z)- and (E)-1-tert-butyl-2-chloroethene (Z/E = 1/12), k = 1.4 x 10(7); neopentylfluorocarbene to (Z)- and (E)-1-tert-butyl-2-fluoroethene (Z/E = 1/2.5), k = 2.6 X 10(6); cyclobutylchlorocarbene to 1-chlorocyclopentene (C migration) and chloromethylenecyclobutane (H migration), k(c) = 4.6 X 10(7), k(H) = 2.1 X 10(7); cyclobutylfluorocarbene to 1-fluorocyclopentene (C migration) and fluoromethylenecyclobutane (H migration), k(c) = 1.8 x 10(6), k(H) = 5.3 x 10(5); cyclopropylchlorocarbene to 1-chlorocyclobutene, k = 9 x 10(5); cyclopropylfluorocarbene to 1-fluorocyclobutene, k = 1.4 x 10(5). Activation energies for several of these processes were in the range of 2-4 kcal/mol, with A approximately 10(8)-10(9) s-1.
Activation parameters for a 1,2 carbon shift in a carbene rearrangement
作者:Robert A. Moss、Guo Jie Ho、Shilan Shen、Karsten Krogh-Jespersen
DOI:10.1021/ja00160a059
日期:1990.2
A new synthesis of 3-fluoro- and 3-chlorocyclobutenes from dihalocyclobutanes. The five isomers of chlorofluorocyclobutane
作者:Norman C. Craig、Steven S. Borick、Michael A. Fisher、Thomas R. Tucker、Yong-Zhuang Xiao
DOI:10.1016/s0022-1139(00)82413-6
日期:1992.11
3-Fluorocyclobutene (1) and 3-chlorocyclobutene (2) have been obtained by simpler syntheses and in higher yield than previously reported. One of the synthetic steps involves a three-phase-transfer-catalysis technique that could be of wider utility. New examples are cited of applying AgF2, an underutilized reagent, as a fluorinating agent near room temperature. Compounds 1 and 2 have been characterized by mass, NMR and vibrational spectroscopies. The NMR spectra have been fully analyzed. Useful group frequencies in the vibrational spectra of halocyclobutenes have been identified. The five monochloro-monofluorocyclobutane precursors of fluorocyclobutenes have also been separated and characterized. From NMR coupling constants, conformer mixtures have been identified for three of the isomers.
Elusive carbenes. Olefinic capture of cyclopropylchlorocarbene and related species