Isomerization nitrogen-containing compounds

Enamines are usually unstable compounds, especially primary ones. By contrast, enamine radical cations as produced by electron ionization (El) in the source of a mass spectrometer have been found to be very stable by recent ab initio calculations1. Among isomeric nitrogen-containing hydrocarbon radical cations with one degree of unsaturation, [C H2w+iN] +, ionized enamines and cycloalkylamines are the most stable these isomers lie usually in deep wells on the potential energy surface, and may also... 

The great structural diversity of nitrogen-containing compounds, ranging from imines and azo compounds to nitro compounds and amines, is connected to its diverse but characteristic photochemical reactivity (Table 6.15). The presence of a lone electron pair on nitrogen in chromophores containing an N=X bond (X=N, C) indicates that both the n,Jt and n,n excited states can be involved in the reactions. While E Z isomerization is a typical reaction for both imines and azo compounds (entry 1), the latter chromophores may additionally... 

After short time heating of maltose in the presence of amines (30 min. at lOO C) the early maltose products predominate (Figure 8). 1-DG deconq>oses mainly to the 3-furanone, -pyranone and its isomerization product cyclopentenone. Further degradation products such as glucosyl isomaltol or nitrogen containing compounds like pyridinium betaine and acetylpyrrol are detected in smaller amounts. The latter request incorporation of amines into early intermediates like 1, 2 or 3. 

These are subdivided into (a) compounds isomeric with aromatic compounds in which the ring contains two double bonds but also an hybridized carbon (7 systems Scheme 6) or a quaternary nitrogen atom (9 systems Scheme 7). 

Isomerization of unsaturated nitrogen-containing organic compounds, containing C=C double bonds, has been investigated less intensely than the isomerization of other related unsaturated compounds. Photoisomerization has been reported upon irradiation of a benzene solution of aqueous solution of its hydrochloride, and of the methiodide salt under nitrogen atmosphere. The corresponding cis-isomers are formed.308,309... 

Scheme 2. Enantioselective isomerization of allyl compounds bearing oxygen or nitrogen containing groups.

Zeolites are known to catalyze the formation of various nitrogen-containing aromatic ring systems. Examples include the synthesis of pyridines by dehydrogenation / condensation / cyclization of C -Cg precursors [1], the formation of methylpyridines by high-temperature isomerization of anilines [2], the amination of oxygen-containing heterocyclic compounds [3] and the Fischer indole synthesis [4,5]. The latter synthesis consists (see Scheme 1) of a condensation towards a phenylhydrazone followed by an acid-catalyzed cyclization with elimination of ammonia. The two reaction steps are usually combined in a one-pot procedure. 

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