Hydrogen bromide with epoxides

It appears necessary to effectively remove the residual o-xylenc during this distillation in order that it not interfere (by liberation of hydrogen bromide) with the subsequent bromination of the epoxide. The checkers used a spinning-band column for this distillation. 

Oxirans. - The synthesis of l,2-anhydro-3,4-di-0-benzyl-6-deoxy-a-D-glucopyranose and its conformational analysis have been reported. A range of epoxides have been prepared by base treatment of bromohydrins, which were made by reaction of hydrogen bromide with aldonolactones. A one-pot conversion of vicinal diols into epoxides employs halohydrin ester intermediates generated from cyclic orthoacetates and either acetyl bromide or trimethylsilyl chloride. Levoglucosenone has been transformed into l,6 3,4-dianhydro-p-D-talopyranose by way of a trn/w-iodo-acetoxylation of the alkene moiety... 

Iodine-catalysed hydroperoxidation of cyclic and acyclic ketones with aqueous hydrogen peroxide in acetonitrile is an efficient and eco-friendly method for the synthesis of gem -dihydroperoxides and the reaction is conducted in a neutral medium with a readily available low-cost oxidant and catalyst.218 Aryl benzyl selenoxides, particularly benzyl 3,5-bis(trifluoromethyl)phenyl selenoxide, are excellent catalysts for the epoxidation of alkenes and Baeyer-Villiger oxidation of aldehydes and ketones with hydrogen peroxide.219 Efficient, eco-friendly, and selective oxidation of secondary alcohols is achieved with hydrogen peroxide using aqueous hydrogen bromide as a catalyst. Other peroxides such as i-butyl hydroperoxide (TBHP), sodium... 

Epoxides from ic-diols. The reaction if secondary, primary v/c-diols with a mixture of 6 M hydrogen bromide in HOAc n suits in a vR -2-acetoxy-l-bromoalkane, which is converted into an alkyloxirane on treaiment with base. The method is suitable for preparation of chiral alkyloxiranes. 

In the second approach, 16-dehydropregnenolone was employed, the double bond of which at the 16,17- position was epoxidised, the epoxide cleaved with hydrogen bromide to the bromohydrin which was reduced and following formation of the 3-formoxy derivative, acetylation of the 17-hydroxy compound gave an intermediate which was oxidised by the Oppenauer reaction to give cortexolone (56) as the diacetate to which the microbiological oxidation could be applied. The process is outlined. 

Hydrogen bromide-catalysed rearrangement of lupenyl acetate affords the olefin (104) which is readily isomerized to (105). Epoxidation of the latter gave the a-epoxide (106), whose structure was confirmed by X-ray analysis. Hydro-boronation of 3/3-acetoxy-30-norlup-19-ene (107) results in addition from the a-face with formation of the 19aH-alcohol (lOS). " The corresponding ketone (109), which undergoes facile epimerization at C-19 in base, was converted into 19aH-lupeol (110), whose spectroscopic properties cast doubt on the recent... 

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