Recent advances in stereoselective bromofunctionalization of alkenes using N-bromoamide reagents (original) (raw)
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Catalytic, Asymmetric Halofunctionalization of Alkenes-A Critical Perspective
Angewandte Chemie International Edition, 2012
Despite the fact that halogenation of alkenes has been known for centuries, enantioselective variants of this reaction have only recently been developed. In the past three years, catalytic enantioselective versions of halofunctionalizations with the four common halogens have appeared and although important breakthroughs, they represent just the very beginnings of a nascent field. This Minireview provides a critical analysis of the challenges that accompany the development of general and highly enantioselective halofunctionalization reactions. Moreover, the focus herein, diverges from previous reviews of the field by identifying the various modes of catalysis and the different strategies implemented for asymmetric induction.
Novel bromination reagents · hexabromocyclopentadiene: bromination of activated saturated sites
Tetrahedron Letters, 1984
Hexabromocyclopentadiene (HBC) readily brominates a-keto and benzylic sites, apparently by bromonium ion transfer. We have recently shown' that hexabromocyclopentadiene (HBC)(l) is a new and useful aromatic bromination reagent in that it performs site-selective electrophilic bromination of activated (electron rich) aromatic compounds. This was postulated to occur by bromonium ion release by virtue of aromatic stabilization of the cyclopentadienide counterpart which ends up as pentabromocyclopentadiene (2). We wish to report now that HBC(1) readily brominates ketones in a-position and alkyl aromatics in benzylic position, as shown in the Scheme and detailed in the Table. We tried aliphatic-(entries l-7), aromatic-(8-12), alicyclic-(13-17), B-dicarbonyl(l8-21) and a,@unsaturated(22,23) ketones and a small number of a-methylene aromatics (entries 24-27) using varying amounts of HBC. As before', the reactions were strongly dependent on solvent polarity; we worked in acetonitrile solutions at two temperatures: 70°C at which analytical/ kinetical runs were performed and monitored by NMR (in MeCN-d3) and at reflux (82°C) with
Catalytic, Enantioselective Syn-Diamination of Alkenes
2019
The enantioselective, vicinal diamination of alkenes represents one of the stereocontrolled additions that remains an outstanding challenge in organic synthesis. A general solution to this problem would enable the efficient and selective preparation of widely useful, enantioenriched diamines for applications in medicinal chemistry and catalysis. In this Article we describe the first enantioselective, syn-diamination of simple alkenes mediated by a chiral, enantioenriched organoselenium catalyst together with a N,N’-bistosyl urea as the bifunctional nucleophile and N-fluorocollidinium tetrafluoroborate as the stoichiometric oxidant. Diaryl, aryl-alkyl, and alkyl-alkyl olefins bearing a variety of substituents are all diaminated in consistently high enantioselectivities selectivities but variable yields. The reaction likely proceeds through a Se(II)/Se(IV) redox catalytic cycle reminiscent of the syn-dichlorination reported previously. Furthermore, the syn-stereospecificity of the tra...
cis-Bromination of Encapsulated Alkenes
Angewandte Chemie International Edition, 2003
Metalated container molecules are currently attracting much interest, since their properties are often different from those of their constituent components. [1-3] Several groups have already reported that such assemblies show a higher chemical reactivity than their unmodified analogues, [4-6] but so far it is unclear, whether they are also applicable in stereoselective transformations. [7, 8] This led us to study the bromination of encapsulated alkene ligands in complexes of the type A (Scheme 1); we hoped that the binding pocket would exert an
Tetrahedron Letters, 2005
A regioselective and highly efficient method for bromination of aromatic compounds in the presence of a stoichiometric amount of hexamethylenetetramine-bromine (HMTAB) as an efficient reagent in dichloromethane is reported. The selectivity depends on the temperature and nature of the substituent on the substrate. The reactivity of this reagent was increased by supporting it to silica gel for bromination of less activated compounds.