Isomerization with iodine/benzene

On the other hand, 2-arylthiazoles are easily isomerized to 3-aryliso-thiazoles in 407o yield upon irradiation with a high-pressure mercury lamp, in benzene solution in the presence of iodine (738). A valence bond isomerization was proposed among several alternatives to account for these results. 

Isomerically pure chlorofullerene C oClg has been reported to be the predominant product of the reaction of with an excess of iodine monochloride in benzene or toluene at room temperature (Scheme 9.11) [79], The product is very soluble in benzene, carbon disulfide and tetrachloromethane. Deep orange crystals can be obtained by recrystallization from pentane. The synthesis of CjoClg using toluene as a solvent proceeds more slowly than with benzene, indicating that radicals are involved and are scavenged by the toluene [79],... 

One of the best known reactions of 1-azirines is the acid/catalyzed hydrolysis to aminoketones. Since the Neber reaction also accomplishes this same synthetic end, this reaction may appear to have little practical value. This is not the situation because with the Neber reaction there is no control over the aminoketone that will be obtained from a given ketone. For example, when oxime (127) derived from benzyl methyl ketone (126) is subjected to the Neber reaction aminoketone 128 is obtained.59 The amino function is substituted for the most acidic a-hydrogen. The isomeric aminoketone (132) that could not be prepared by the Neber reaction can be formed by the hydrolysis of 1-azirine (131). The synthesis of this 1-azirine has been accomplished from allyl benzene (129) through vinyl azide (130) using iodine azide.22... 

Bis(iodosyl)benzene reacted with triflic anhydride to afford a bis iodine (III) derivative [21], DIB or iodosylbenzene, however, do not afford with triflic acid, or its anhydride, the expected analogues of HTI, although these are initially formed. The reaction of iodosylbenzene and triflic anhydride leads to two different products, depending on reaction time. When triflic acid was allowed to react with iodosylbenzene in dichloromethane for about 20 min the yellow p-compound 1 (m.p. 100-110°C) was obtained it was the same with the so-called Zefirov s reagent, which was originally prepared from DIB and triflic acid in chloroform. When the reaction time was extended to 12 h, then 1 isomerized to the slightly pale yellow compound 2 (m.p. 125-132°C). For preparative purposes the direct reaction of iodosylbenzene with triflic acid was preferable for 2, since it was isolated in 94% yield. 

Aromatic systems substituted with electron-donating groups are more readily halogenated than benzene. Consequently, other synthetic routes or reagents are sometimes used to avoid polyhalogenation and the formation of isomeric mixtures. For example, the iodination of toluene gives a mixture of 2- and 4-iodotoluenes each isomer can be prepared individually from the appropriate toluidine via the diazonium salt (see Chapter 8). 

Acetonation of 3-0-methyl-D-glucitol affords the isomeric 1,2 5,6-and 2,4 5,6-di-0-isopropylidene derivatives which are differentiated on silica gel layers [hRf 50 and 25, respectively, in benzene-methanol (90 + 10)] with visualization by iodine vapor [85]. The four stereoisomers of l,2 5,6-di-0-trichloroethyUidene-a-D-glucofuranose, which differ in the configuration of the acetal carbons atoms, are resolved on silica gel with ethyl acetate-petroleum ether (b. p. 40—50°) (50 + 50) [86]. Chloroform-acetone (97 + 3) and benzene-ether (90 + 10) have been used to separate mixtures of acylated di-O-isopropylidene-hexitols [87, 88]. 

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