Regio- and stereoselective synthesis of bromoalkenes by homolytic hydrobromination of alkynes with hydrogen bromide

Selective C−H Halogenation of Alkenes and Alkynes Using Flavin‐Dependent Halogenases

“…We hypothesized that in the absence of the substrate nucleophile, halosubstitution involving water as a nucleophile or perhaps olefin C−H halogenation could be possible using FDHs, in analogy to the corresponding halocyclization and native C−H halogenation reactions (Figure 1C). Despite the utility of haloalkenes for cross‐coupling and other applications, accessing these compounds in a stereoselective manner typically requires functional group interconversion processes, and selective halogenation of 1,1’‐disubstituted olefins remains rare [37–39] . Direct synthesis of brominated styrenes through C−H functionalization has been reported, but 1,1’‐disubstituted substrates were either not discussed, [40] or lead to mixtures of cis‐ and trans‐brominated products [41,42] .…”

“…Despite the utility of haloalkenes for cross-coupling and other applications, accessing these compounds in a stereoselective manner typically requires functional group interconversion processes, and selective halogenation of 1,1'-disubstituted olefins remains rare. [37][38][39] Direct synthesis of brominated styrenes through CÀ H functionalization has been reported, but 1,1'-disubstituted substrates were either not discussed, [40] or lead to mixtures of cis-and transbrominated products. [41,42] Stereoselective CÀ H halogenation of alkenes would therefore represent a particularly useful target for FDH catalysis.…”

Recent Progress in Haloalkene Synthesis by Hydrohalogenation (HX=HCl, HBr, HI) of Alkynes

“…Miura and coworkers recently reported that the homolytic reaction of HBr can be controlled by using HBr/AcOH in lesspolar toluene solution. [47] The reaction basically undergoes anti-Markovnikov selectively to afford E-bromoalkene E-3 Br when an arylacetylene 1 was used as a substrate. On the other hand, for alkylacetylenes 1, a stereoselective control is not achieved despite several attempts, while the regioselectivity is controlled enough.…”

Lewis acid catalyzed Markovnikov hydrobromination and hydrochlorination of alkynes using TMSX (X = Br, Cl)

“…Ideally, HX (X = Br, Cl) were used as reagents in these reactions and the reaction could occur under mild conditions. [14][15][16][17][18][19][20] However, these two reagents are irritating gases (sometimes corrosive and toxic) in their pure form and extra care should be taken when handling them. The solution of these reagents in water or acetic acid is commercially available, yet they may be problematic when used in organic reactions due to severe side reactions.…”