Deamination conformational control

The pinacolic deamination of 2-amino-1,1 -diaryl-1 -propanols provides a convincing case for conformational control. Optically active 2-amino-l,l-diphenyl-l-propanoI 209) affords a-phenylpropiophenone (210) with 88% inversion plus 12% retention (76% inversion plus 24% racemization) at the terminus of phenyl migration 196K The diastereomer (211) of 2-amino-l-anisyl-l-phenyl-l-propanol reacts with preferential... 

The deamination of 3-phenyl-2-butylamines,(J57), X=NH2, differs strongly from the solvolysis of the corresponding tosylates (Table 13)200. As pointed out previously, these reactions are conformationally controlled (Section 6.2). With the erythro diastereomer, the tram orientation of phenyl and amino (diazonium) groups is conformationally favored. A high yield of optically active erythro product results. With the threo diastereomer, phenyl participation is conformationally disfavored. Threo and erythro products are obtained in comparable quantities, and with partial race-mization, indicating the dominance of the kc pathway. 

We start this section with a short discussion of conformational control, because conformations of alkylamines and alkanediazonium ions are important factors for the deamination mechanisms. The distribution and configuration of products is often a function of the relative population of conformers. If two conformers yield two different products basically two cases have to be distinguished ... 

As discussed in Section 7.4, conformational control in deamination of open-chain amines is difficult to evaluate because the activation energies of conformational changes are often smaller than those of the steps in deamination reactions. Alicyclic amines are more suitable for such mechanistic investigations. In addition, the con-formers of such amines can be locked if they contain bulky substituents (tert-hvXyX) or if the amines are based on bi- and polycyclic hydrocarbons (decalinamines, cholestaneamines, norbornylamines, etc.). We shall therefore concentrate first on the deamination of the epimeric 4-( er butyl)cyclohexylamines. Then, we will discuss the structural problems of cyclic carbocations formed in deamination of norbor-nylamine, cyclopropylmethylamine, and cyclobutylamine, i. e., compounds that are at the center of interest in the debate on classical versus nonclassical carbocations. 

Undoubtedly, the vicinal groups play a fundamental role in the outcome of this reaction, especially with the sugars, where the favored conformation of the molecule at equilibrium is controlled at the outset by groups that determine whether the molecule exists as a cyclic or acyclic structure. The deamination of cyclic and acyclic amino sugar derivatives by nitrous acid will be considered in turn. 

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