- Promotion of Appel-type reactions by N-heterocyclic carbenes
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N-Heterocyclic carbenes (NHCs) have been extensively used as a versatile class of catalysts and ligands in organocatalytic and organometallic chemistry. However, there are only a small number of synthetic applications where they act as reagents. Here we demonstrate that NHCs can be used as stoichiometric redox reagents for Appel-type halogenation reactions of alcohols. This new reactivity reveals a fresh and interesting aspect and enriches the chemistry of NHCs in an underexplored area. The potential of performing this chemical transformation at the catalytic level using an NHC-oxide derivative is also investigated.
- Hussein, Mohanad A.,Nguyen, Thanh Vinh
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supporting information
p. 7962 - 7965
(2019/07/12)
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- Visible-light-promoted Wohl-Ziegler functionalization of organic molecules with N-bromosuccinimide under solvent-free reaction conditions
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The visible-light-induced transformation of toluenes with N-bromosuccinimide (NBS) under solvent-free reaction conditions (SFRC) was studied. The reaction took place in spite of the very restricted molecular motion; toluenes could be regioselectively converted to benzyl bromides. Selective radical-chain reactions with NBS were carried out in liquid/liquid and in solid/solid systems; furthermore, reactions could be performed in the presence of air. The radical scavenger TEMPO (=2,2,6,6-tetramethylpiperidin-1- yloxy) completely suppressed the side-chain bromination of toluenes with NBS under SFRC. Electron-withdrawing groups decreased the reactivity of the toluenes, and the Hammett reaction constant ρ+ = -1.7 indicated involvement of polar radical intermediates with electrophilic character.
- Jereb, Marjan,Zupan, Marko,Stavber, Stojan
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experimental part
p. 555 - 566
(2009/09/06)
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- Release tag compounds producing ketone signal groups
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A release tag reagent suitable for use in the chemical analysis of a substance to be detected comprises signal, release, and reactivity groups. A class of release tag compounds that are cleaved to release as signal groups very stable electrophoric ketones which are sufficiently volatile for determination in the gas phase of an analytical reaction mixture is disclosed.
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- An Investigation of Potential -Sigmatropic Rearrangements of Pentafluorophenyl-aza-, -thio-, and -methylene-sulphonium Ylides
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The reactions of pentafluoroaniline and pentafluorothiophenol with dimethyl sulphoxide-trifluoroacetic anhydride at low temperatures followed by triethylamine give the N-trifluoroacetyl compound (6) along with the N-trifluoroacetyl-N-methylthiomethyl compound (7) and decafluorodiphenyl disulphide, respectively; no molecular rearrangements occur.Under similar conditions 2,3,4,5,6-pentafluoro-N-methylaniline gives the cyclohexa-2,5-dienone derivative (8) via hydrolysis of the -sigmatropic rearrangement intermediate (9). 2,3,4,5,6-Pentafluorobenzyl bromide and dimethyl sulphide give the sulphonium compound (10) which with butyl-lithium in tetrahydrofuran gives four products derived from the highly reactive -rearrangement intermediate (17): (11) (32percent), (12) (2.5percent), (13) (5percent), and (14) (11percent).One product only (21) (6percent) derived from (17), could be isolated from the reaction in ether.Dimethylsulphonium methylide reacts with hexafluorobenzene to give a much simpler product consisting of (13) (5percent) and (14) (45percent).
- Brooke, Gerald M.,Ferguson, J. A. K. Jamie
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p. 2023 - 2026
(2007/10/02)
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