Bromohydrin coupling reactions

Araki and co-workers have reported the [Pd(PPh3)4]-catalyzed cross-coupling reaction of isoprene bromohydrin with heteroaromatic organolithium reagents in good yields without rearrangement (Scheme Pelter and co-workers have reported that the [Pd(PPh3)4]-... 

Acetoxyiodination of cyclohexene derivatives is acquired by the oxidative combination NCS/Nal/AcOH427. NBS/AcOH is the common reagent for acetoxybromination428. N-Bromoacetamide in acetic acid or water reacts with 1 l,12-dihydrobenzo[e]pyrene to yield the corresponding bromoacetate and bromohydrine, respectively429. KBr can also be used under oxidative conditions, e.g. coupled with peracid and 18-crown-6430. Iodo enol acetates are obtained by reaction of bis(pyridine)iodo tetrafluoroborate with acetylenes in acetic acid (equation 51)431. 

Preparation (b). The reaction sequence is shown in the formulation. Treatment of paraldehyde and absolute ethanol with hydrogen chloride gas at —5° produces a-chloroethyl ethyl ether (1), which on bromination affords a,j8-dibromoethyl ethyl ether (2). Coupling with allylmagnesium bromide gives (3), which on reaction with zinc dust in n-butanol generates 1,4-pentadiene. Thus one double bond is that of allyl bromide, and the other is generated by elimination of BrOCjH, from the bromohydrin ethyl ether (3). 

As outlined in Scheme 6, isovanillin (35) was converted to aryl iodide 36 via MOM-protection, protection of the aldehyde, and subsequent iodination. Hydrolysis of the acetal and Wittig olefination delivered phenol 37 after exposure of the intermediate aldehyde to methanolic hydrochloric acid. Epoxide 41, the coupling partner of phenol 37 in the key Tsuji-Trost-reaction, was synthesized from benzoic acid following a procedure developed by Fukuyama for the synthesis of strychnine [62]. Birch reduction of benzoic acid with subsequent isomerization of one double bond into conjugation was followed by esterification and bromohydrin formation (40). The ester was reduced and the bromohydrin was treated with base to provide the epoxide. Silylation concluded the preparation of epoxide 41, the coupling partner for iodide 37, and both fragments were reacted in the presence of palladium to attain iodide 38. 

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