Methanolic sodium hypobromite

Reduction of nitrobenzene in methanolic or ethanolic sodium hydroxide solution with zinc powder leads to azobenzene or hydrazobenzene according to the proportion of zinc powder employed (Expts. 6.90 and 6.91). Hydrazobenzene may be oxidised to azobenzene by sodium hypobromite solution at 0 °C. 

The first asymmetric total synthesis of the hasubanan alkaloid (+)-cepharamine was completed by A.G. Schultz et al. In order to construct the c/s-fused A/-methylpyrrolidine ring, the advanced tetracyclic lactone was first converted to the primary carboxamide by treatment with sodium amide in liquid ammonia. Next the Hofmann rearrangement was induced with sodium hypobromite in methanol initially affording the isocyanate, which upon reacting with the free secondary alcohol intramolecularly gave the corresponding cyclic carbamate in excellent yield. 

Methyl 3-bromopropiolate has been prepared by esterification of 3-bromopropiolic acid with methanol and sulfuric acid for 6 days (75% yield)the starting bromo acid being prepared by bromination of propiolic acid with aqueous potassium hypobromite. This reaction is particularly delicate to control, giving erratic results. Moreover, direct bromination of methyl propiolate with sodium hypobromite could not be reproduced. 

The low yields attending the rearrangement of unsaturated amides have been attributed " to interference by the reaction just discussed coupled with oxidation of the double bond by the hypobromite present. The products of oxidation have not been isolated and characterized, however. Such reactions may be avoided with a,/3-unsaturated amides by employing methanolic sodium hypochlorite (p. 282), but the action of this reagent on other types of imsaturated amides has yet to be investigated. 

Several new methods for the preparation of 1-haloalkynes have been described. High yields of bromo compounds, e.g. 28, are obtained by treatment of alkynes with triphenylphosphine/carbon tetrabromide, or with a concentrated aqueous solution of potassium hypobromite and potassium hydroxide (equation 1). 1-Iodoalkynes are produced from terminal alkynes and bis(pyridine)iodine(I) tetrafluoroborate in methanol in the presence of sodium methoxide (equation 2) or from alkynes with a mixture of iodine, potassium carbonate, copper(I) iodide and tetrabutylammonium chloride under phase-transfer catalysis. Lithium acetylides 29 (R = Ph, t-Bu, HOCH2 etc.) react with zinc iodide and bis(trimethylsilyl) peroxide to yield 1-iodoalkynes. The method has been... 

However, the cyclization of pyridine with hypobromite in methanol was not accompanied by bromination of IP-2-ones. In contrast, the reaction of 6-oxy-2-amino-nicotinamide with sodium hypochlorite provided 6-chloro-IP-2,4-dione (57AP20). 

The closing sequence comes from Kenner C. Rice and comprises seven stages. [103] Acetalisation of the keto-function and elimination of methanol with p-toluenesulfonic acid in chloroform is followed by addition of methyl hypobromite. Ehmination of HBr and hydrolysis of the ketal leads to the unsaturated ketone, which is reduced stereoselectively with sodium borohydride to produce (-)-codeine. This generates the fifth stereogenic centre. The methyl ether is finally cleaved with boron tribromide. 

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