Nitroso compounds give imines

Trifluoromethyl-substitutedazimines are surprisingly stable compounds. They are accessible by 1,3-dipole metathesis from tnfluoromethyl-substituted azomethine imines and certain nitroso compounds [187, 188] On photolysis, an electrocyclic ring closure first gives the triaziridines, which are stable at room temperature. On heating above 80-100 C, a valence tautomenzation takes place and azimines are formed [189] (equation 43). 

A variety of double bonds give reactions corresponding to the pattern of the ene reaction. Those that have been studied from a mechanistic and synthetic perspective include alkenes, aldehydes and ketones, imines and iminium ions, triazoline-2,5-diones, nitroso compounds, and singlet oxygen, 10=0. After a mechanistic overview of the reaction, we concentrate on the carbon-carbon bond-forming reactions. The important and well-studied reaction with 10=0 is discussed in Section 12.3.2. 

In a study of the chemistry of oxaziranes [75], it was discovered that this class of novel heterocyclic compounds is readily oxidized with peracetic acid to give dimeric nitroso compounds. Since the oxaziranes are, in turn, prepared by a peracetic acid oxidation of imines, the crude imines can, by proper adjust-... 

Reaction of nitroso compounds with active methylene groups to give imines [46a, b]. 

Alkylidene triphenylphosphoranes react with nitroso compounds to give imines [54]. 

Secondary amines can be oxidized at the N-H bond to hydroxylamines and nitroxides, and via nitrones via C-N oxidation. Nitrones are valuable intermediates in the production of isoxazolines. Initial C-N oxidation of secondary amines gives imines which can react further to oxaziridines. The latter can be converted to nitrones, and both to amides. Primary amines are oxidized at the N-H bond to mono-substituted hydroxylamines, which are readily converted further to nitroso and nitro compounds by the more activated peroxygen... 

Intramolecular alkylation of oximes. Fuchs etal. reasoned that C-alkylation of oximes to give nitroso compounds should be possible when O- or N-alkylation would lead to strained imines. Thus treatment of the oxime tosylate (2) with 1 in a homogeneous reaction results in ring contraction to 3, presumably through a nitrosocyclopropane intermediate a. The reaction with bases insoluble in THF is much slower. 

Although reactions with N=0 derivatives do not formally fall into this category of reactions, it is somewhat related. Nitroso compounds react with activated nitriles in the presence of LiBr and microwave irradiation to give a cyano imine, ArN=C(CN)Ar. This transformation has been called the Ehrlich-Sachs reaction ... 

Since oximes are reduced to imines with buffered aqueous TiCb, one can assume that reduction of nitronate anions might progress through a similar mechanism. With regard to the reduction of nitro compounds themselves, there is some evidence for the intermediacy of a nitroso compound (178 Scheme 43). Indeed, at low pH tautomerization of (178) to oxime (179) would be rapid, whereas with TiCb-NH4OAC at pH 6 the nitro group is trapped to give only pyrroline (183), due to slow tautomerism. 

Primary amines RNH2 (R = i-Pr, /-Bu, t-Bu or cyclohexyl) react with the carbamate Et02CN=CCl2 to yield the carbodiimides Et02CN=C=NR. A new method of preparing imines is to add a carbonyl compound (2,6-dimethylcyclohexanone, 2-tetralone, 2-decalone etc.) to a preformed complex of a primary amine (t-butylamine, cyclohexylamine, benzylamine or 1-phenylethylamine) and titanimn(IV) chloride suspended in hexane or octane. Primary amines R NH2 (R = t-Bu, N=C, Tos or phthalimido) react with nitroso compounds R NO (R = r-Bu, pyrrolidin-l-yl, Ph or 2-MeCC6H4) in the presence of the hypervalent iodine compound Phi (OAc)2 to give... 

N-oxidation can occur in a number of ways to give either hydroxylamines from primary and secondary amines [Eqs. (11) and (12)], hydroxamic acids from amides, or N-oxides from tertiary amines [Eq. (13)]. The enzyme systems involved are either cytochrome P450 or a flavoprotein oxygenase. Hydroxylamines may be further oxidized to a nitro compound via a nitroso intermediate [Eq. (11)]. Oximes can be formed by rearrangement of the nitroso intermediate or N-hydroxylation of an imine, that could in turn be derived by dehydration of a hydroxylamine [Eq. (11)]. N-Oxides may be formed from both tertiary arylamines and alkylamines and from nitrogen in heterocyclic aromatic systems, such as a pyridine ring. 

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