Hydrides nitrenium ions

A different method of generating a nitrenium ion has been demonstrated the sulfur-nitrogen bond in (55) cleaves and then a novel intramolecular hydride shift to the arylnitrenium ion centre takes place. The nitrenium species (56) undergoes two nucleophilic additions to the double bond to give the product (57). Two studies concerning the physiological effects of nitrenium ions in vivo are reported. Products are formed from both the ion-paired nitrenium ion (59) and the free ion (60)... 

By analogy to carbenium ions, it can be expected that alkylnitrenium ions will experience 1,2-alkyl and hydride shifts. These would presumably be orbital symmetry allowed reactions that convert the nitrenium ion into a more stable iminium ion. This idea is supported by several theoretical studies suggesting that simple... 

The observation of apparent 1,2-alkyl and hydride shift products was the basis of much discussion of alkylnitrenium ion chemistry several decades ago. In fact, several reactions (e.g.. Fig. 13.12) reported by Gassman and others, were ascribed to nitrenium ions. Unfortunately, it is in practice very difficult to determine whether such products resulted from reaction of a free nitrenium ion or whether they occurred conceitedly with the dissociation of the leaving group. 

Srivastava et al. showed that the parent nitrenium ion is capable of adding to simple aromatics such as benzene, toluene and anisole (91) to give aniline derivatives (92a-c, Fig. 13.47). Unfortunately, these reactions give a distribution of regio-isomers as well as products derived from competing hydride and/or hydrogen atom transfer. 

Treatment of imidazo[2,l-A [l,3,5]benzotriazepines 79 with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in acetonitrile at ambient temperature resulted in oxidative ring contraction with formation of stable (dihydroimidazo-lybbenzimidazoles 80 (Scheme 15). The reaction was suggested to occur via the initial hydride abstraction from N(6) followed by triazepine ring scission and formation of nitrenium ion <2005FA127>. 

Hydride shift, 84 in carbenes, 115 in carbocations, 107 in nitrenes, 118 in nitrenium ions, 120... 

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