Hydrobromination of alkynes with

The stereospedfic and regioselective hydrobromination of alkynes with chlorobis(T -cyclopentadienyl)hydrozirconium and NBS produces ( )-vinylic bromides in good yields. The bromine atom usually adds regioselectively to the carbon atom that bears the smaller substituent and stereoselectively trans to the larger substituent (D.W. Hart, 1975 M. Nakatsuka,... 

OH/Br exchange (aq. HBr/PBr3), 303 porphyrin synthesis with, 255, 349 Hydrobromination of alkynes with Zr, 132, 325 Hydrochlorothiazide, 310 Hydrofluoric acid aq. HF) deblocking with of diol acetonides, 277 of silyl ethers, 277, 329 of silyl thioethers, 169 Hydroformylation of alkenes, 46-48 Hydrogenation, 96-105 See also Hydrogenolysis) of alkenes, 41, 96-97, 101-103, 278, 283 of alkynes to (Z)-alkenes, 40, 64,100-101... 

The rate of hydrobromination of PhC=CH in 90% AcOH at initial concentrations of 0.1 -1.0 M can be described by third-order (time) and first-order (concentrations) reaction equations with respect to the alkyne. The dependence of on the initial reactant concentration passes through a minimum, which is always present when the ionic strength fi of the solution is maintained at 1.1, and is due to the participation in the reaction of several types of species formed by HBr. From the dependence of on the degree of dissociation of HBr ion pairs by the Acree equation, the /cion was estimated at 1 x 10 1 moH s. Since HBr ion pairs do not react with phenylacetylene, the authors proposed that, at high concentrations, the reaction involves hydrogen bromide dimers. ... 

Vinyl Halides. The Wittig reaction of bromomethylene triphenylphosphorane with aldehydes is an acceptable route to mainly (Z)-l-brome-alkenes if potassium t-butoxide is used as base to form the ylide. ° 2-Bromo-l-atkenes have been prepared by Markovnikov hydrobromination of 1-alkynes with tetraethylammonium hydrogen dibromide (Et4N HBr2)."°... 

Need to effect a formal hydrobromination of an alkyne with Markovnikov selectivity... 

---

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

---