Carbon-nitrogen skeleton rearrangement

An intermediate aziridinium ion accounts for the observation that alkylations with /S-haloalkyl tertiary amines frequently lead to products with a rearranged carbon-nitrogen skeleton. For example. l-dialkyl-arruno2-jsubstitufc d propanes may form 2-dialkylamino-l-subBtituted... 

Thermal decomposition of quaternary ammonium salts and bases is most valuable in structural investigations of amines, particularly heterocyclic secondary amines (Hofmann exhaustive methylation). The course of the elimination (A or B) is determined by the nature of the four alkyl groups on the nitrogen atom. The reaction has found little use in the synthesis of pure olefins. The yields are low even when three of the alkyl groups are methyl radicals. Carbon-skeleton rearrangement does not occur. Thus, the only olefin obtained by pyrolysis of pinacolyltri-methylammonium hydroxide, (CHj),CCH(CHj)N(CHj)j OH, is /-butylethylene (50%). ... 

Birch reduction of acid derivatives is even more productive if the first-formed enolate (as 66) is used as a nucleophile. Our example also links this chapter with the last as a Cope rearrangement is featured. A group of alkaloids including mesembrine have the bicyclic structure 89. Removing the structural nitrogen atom by standard disconnections (chapters 6 and 8) leaves the carbon skeleton 91 that does not immediately look a Birch reduction product. 

The isomerization of 3 into 15 implies the migration of the two substituents from the carbon atom to the two nitrogen atoms, and also a rearrangement of the CNN skeleton. Since under these experimental conditions diazo derivatives usually loose dinitrogen, this complicated process is very surprising One can easily anticipate that the migrating aptitude of the stannyl substituents is a key point of the process. 

This c20 pyrophosphate (122), C20H36O7P2, is thought to provide the carbon framework of the diterpene alkaloids such as veatchine (123), atisine (124), and aconitine (125) (Fig. 5). It is not known at what stage the nitrogen is incorporated into the framework established by the skeleton. The potential for terpene rearrangements and the observation that the alkaloids are frequendy found esterified, often by acetic or benzoic acid, as well as free, has led to permutations and combinations producing over 100 such compounds. 

The chemistry of the Cinchona alkaloids involves a typical reactivity of their fragments such as hydroxyl group at C-9 or vinyl group at C-3 and two basic nitrogen atoms incorporated into quinuclidine and quinoline as well as more specific transformation occurring with a rearrangement of their carbon skeleton. 

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