Ethers hydrobromination

A number of functional groups including sulfones, ethers and even alcohols (occasionally) can be accommodated during hydrobromination. Functional groups in close proximity to the C—C double bond can have an important directing effect (equations 88 and 89).133,134... 

Dehydrobromination.3 One approach to trialkylsiloxyalkynes involves de-hydrobromination of 1, prepared from tribromoethanol, with BuLi (2 equiv.) to form (Z)-2-bromovinyl silyl ethers 2, which can be converted by LDA followed by alkylation into siloxyalkynes (4). These products undergo cycloaddition with vinyl... 

Starting with geraniol (126), Sharpless asymmetric epoxidation [68] proceeded in 95% yield and with 93% ee (see Scheme 29) [69]. Hydrobromination of the alkene was achieved under standard conditions using NBS in THF and water (5 1) to afford a 64% yield of diastereomeric bromo alcohols (127). Cyclization to the tetrahydropyran diol was accomplished by treating 127 with camphorsulphonic acid in diethyl ether, followed by diol cleavage with sodium periodate to give a mixture of aldehydes 128 and 129. Upon... 

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... 

Bromo-l-alkenes can be prepared regioselectively and in high yield by direct hydrobromination of terminal acetylenes with tetraethylammonium hydrogen dibromide in dichloromethane. The reagent, which is prepared in situ from tetraethylammonium bromide and hydrogen bromide, also hydro-brominates acetylenic alcohols and ethers. 

Ethoxylated derivatives of castor oil are also useful as industrial, cosmetic, and food emulsifiers for use in detergents, lubricating and ending oils, hydraulic fluids, and hydraulic fracturing (fracking). Ethoxylation can proceed by heating castor oil and ethylene oxide in the presence of acid or base or via SN2 displacement of bromine from hydrobrominated castor oil or ricinoleate by the sodium base of polyethylene oxide monomethyl ethers, allowing controlled production of ethoxylated castor oil (El-Azab et al., 2010). 

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