Reductive bromination

Diiodosilane reduces acetals to alkyl iodides in a reductive iodination reaction (Eq. 312).358,505 Alkyl bromides are formed from the reductive bromination of benzaldehyde acetals with the combination Et3SiH/SnBr2.506... 

The reduction of epoxides occurs with the reagent combinations Et3SiH/BF3566 and EtjSiH/BI 3 01 T24<)7 The reductive iodination of epoxides is carried out with the combination of TMDO and iodine (Eq. 344).357 The yields are good to excellent. The reductive bromination of epoxides is accomplished in a similar manner. Trimethylchlorosilane is found to enhance these reactions.567... 

Benzyl Bromide [Reductive Bromination of an Acetal].506 To a suspension of tin(II) bromide (5.1 mg, 0.02 mmol) and benzaldehyde dimethyl acetal (54.8 mg, 0.36 mmol) in CH2C12 (2.5 mL) were added successively Et3SiH (65.0 mg, 0.56 mmol) and acetyl bromide (96.8 mg, 0.79 mmol) in CH2C12 (1 mL) at room temperature under an argon atmosphere. The mixture was stirred for 3 hours at room temperature and quenched with a phosphate buffer (pH 7). 

Benzo[e]thieno[3,2- ]thiepin-10(5Ef)-one 388 can be smoothly reduced with sodium borohydride to the corresponding alcohol, which forms the chloro substituted compound under standard treatment with thionyl chloride (1991CPB2564). Dihydro derivatives of pyrrolo-benzothiazepine 377 have been reported starting from ketone 373 by a carbonyl reduction, bromination and amination sequence (Scheme 76, Section 5.1.1 (1998JMC3763, 2002JMC344, 2004JMC143)). 

Reductive brominations were carried out by Gilman and co-workers on lO-ethylphenothiazine-5-oxide and 3-bromo-lO-ethylphenothiazine-5-oxide, and by Bodea et who prepared... 

A particular instance of reductive bromination has been reported by Bodea and Terdic. They brominated phenothiazine-5-oxide with elementary bromine and found that bromophenothiazines are formed, containing one bromine atom more than expected on the basis of the utilized molar ratio. Thus, starting with phenothiazine-5-oxide, on treatment with 1 mole of bromine one obtains 3,7-dibromophenothiazine, with 2 moles of bromine 1,3,7-tribromopheno-thiazine, and with 3 moles of bromine 1,3,7,9-tetrabromophenothia-zine. It was therefore assumed that the first step consists of an electrophilic substitution, leading to 3-bromophenothiazine-5-oxide (54), which immediately undergoes reductive bromination with the hydrobromic acid formed in the first reaction to give 3,7-dibromo-phenothiazine (55). If more bromine is used, 55 is further brominated to the tri- or tetrabromo derivative. 

The synthesized compounds were prepared by means of the Wittig reaction. The appropriate phosphoranes were obtained from commercially available aldehydes (through reduction, bromination, reaction with triphenylphosphine, and treatment with bases) and reacted with the required aldehydes. Mixtures of the E and Z stereoisomers in variable ratios were obtained and separated by chromatography. 

Reductive bromination. Aromatie aldehydes are eonverted into ArCH2Br by these reagents (e.g., isopinocampheylboron dibromide) (12 examples, 65-87%). 

Cyclo-octatetraene.—Synthesis. Full details have been published on the preparation of stable cyclo-octatetraene bond-shift isomers. 1,2,3,8-Tetramethylcyclo-octa-tetraene was prepared from sulphone (140) by dialkylation, reduction, bromination, and dehydrobromination and shown to give Diels-Alder adduct (141 = H,... 

Results of a theoretical study of the mechanism of Br2 oxidation of IH-pyrazolines to pyrazoles suggest that a bromo substituted 2- or 1-pyrazoline is involved in the reaction. Br2 and SbCls oxidize bis(4-t-butylphenyl)nitroxyl (A) to the corresponding oxoammonium salts. The tribromide salt on heating is converted into a mixture of bromodiphenylamines which is also formed from A as a result of three-electron reductive bromination. ... 

Although the reductive bromination of aromatic aldehydes using cyclohexylboron dibromide proceeds at room temperature, the reaction is quite slow. A mechanistic study revealed that the... 

SCHEME 23.49 Pathways involved in reductive bromination reaction. 

KabaUca, G. W., Wu, Z., Ju, Y. 2000. Reductive bromination of aromatic aldehydes using aUcylboron dibromides. Tetrahedron Lett. 41 5161-5164. 

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