Other Unusual Heterocycles

E. Other Unusual Heterocycles Alumatranes and titanatranes 93ACR483. 

Deviations of this magnitude are very unusual but can also be found for other sensitive heterocycles, such as 1,2,5-oxadiazole-2-oxides. Although the authors... 

Certain heterocycles will undoubtedly possess new and unexpected toxicities, yet most of the more esoteric ring systems have yet to be evaluated for toxicity in mammals. An example of how a rare toxicity is sometimes associated with an unusual heterocycle is provided by the potent neurotoxin (41), where relatively firm structural requirements for activity have been defined (76MI10502, 79MI10501). Within this context, the possible toxicity of compounds (42)-(44), for example, becomes interesting, but each of these are of unknown biological activity. Many other examples could be cited and can be readily identified by appropriate searches of the relevant sections of Chemical Abstracts (Sections 004 and 059). 

Some synthetically useful reactions not covered in the above sections should be mentioned. An unusual heterocyclization to form indole derivatives is found in the aminomercuration of allylenaminones (equation 130).261 Palladium(II)-catalyzed cyclizations of o-allyl- and -vinyl-anilines and amino-quinones are discussed elsewhere.30 Other electrophiles used to form dihydroindole derivatives include phenylselenenyl chloride216 and methyl(bismethylthio)sulfonium salts.231... 

Heterocyclic betaines and other unusual structures have been the subject of extensive investigation [88AHC(44)269 92AHC32]. The specific focus of this report is to survey recent progress in the chemistry of heterocyclic betaines and molecules with a betaine character of general type 1 (Scheme 1), and should serve to complement other reviews that deal with heterocyclic betaines of alternant hydrocarbons [80AHC(26)1] and heterocyclic mesomeric betaines (85T2239). 

Structure and Stereochemistry (it is self-subdivided into Theoretical Aspects, Stereochemical Aspects, Betaines and Other Unusual Structures, Miscellaneous Substituted Heterocycles). 

Exchange of the bromine atoms in 142 and 145 for other halides or hetero-atomic groups is similarly facile [100]. Among those listed in Scheme 31, the triazides 154 and 158 are interesting because of their further conversion. Reduction of 154 with lithium aluminium hydride furnishes the C3v-symmetrical triamine 155 [105] (cf. Scheme 33 for the Cs-symmetrical isomer). The homologue 158 was converted into unusual heterocycles by thermolysis [100] (cf. Scheme 43). Three-fold bridgehead ethers such as 159 and 160 were obtained by alcoholysis of 142, and Ag1 ion assisted reaction of 142 with tert-butyl hydroperoxide afforded the tris(peroxide) 161 [100]. 

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