Imine, N-oxides

Oxaziridines are known thermally to revert to imine N-oxides, and it is not surprising that when heated in presence of isocyanides they undergo the equivalent of a [3 +1] addition (79BAU1648). Although the imino 1,2-oxazetidine was not isolated, its intermediacy was inferred from the isolated decomposition products (Scheme 117). 

Buchardt, O., Amine and imine N-oxides, in Houben Weil Handb. Org. Chem. Photochemistry, G. Thieme Verlag, Stuttgart, Vol. 4/5b, 1975, 1282. 

This corresponds with MacDiarmid s observations which show that the second redox step is strongly pH-dependent. MacDiarmid further differentiated his redox model to take account of the fact that pure leucoemaraldine with its amine-N is already protonated at pH values 2, and that the totally oxidized pemigraniline with its less basic imine-N can also be protonated. This gives the following (simplified) reaction scheme ... 

The third variant is that of Genies and Lapowski They base their model on the assumption of fundamental differences between the two oxidation steps in PANI. The first step is analogous to that of MacDiarmid. For the second redox process the authors postulate the additional oxidation of imine-N... 

It is of interest that antibacterial activity can be retained even when the imine carbon-nitrogen bond is replaced by a carbon to carbon double bond. Base-catalyzed condensation of 5-nitrofurfuraldehyde (24) with 2,6-dimethylpyridine (38) affords olefin 39. Treatment of this compound with hydrogen peroxide gives the corresponding N-oxide (40). Heating of... 

The total synthesis of carbazomycin D (263) was completed using the quinone imine cyclization route as described for the total synthesis of carbazomycin A (261) (see Scheme 5.86). Electrophilic substitution of the arylamine 780a by reaction with the complex salt 779 provided the iron complex 800. Using different grades of manganese dioxide, the oxidative cyclization of complex 800 was achieved in a two-step sequence to afford the tricarbonyliron complexes 801 (38%) and 802 (4%). By a subsequent proton-catalyzed isomerization, the 8-methoxy isomer 802 could be quantitatively transformed to the 6-methoxy isomer 801 due to the regio-directing effect of the 2-methoxy substituent of the intermediate cyclohexadienyl cation. Demetalation of complex 801 with trimethylamine N-oxide, followed by O-methylation of the intermediate 3-hydroxycarbazole derivative, provided carbazomycin D (263) (five steps and 23% overall yield based on 779) (611) (Scheme 5.91). 

Abstract This chapter principally concerns oxidations of organic substrates containing N, O, S, P, As and Sb. Oxidations of amines are covered first, including primary amines to nitriles or amides secondary amines to imines or other products tertiary amines to N-oxides or other prodncts (Section 5.1) and the oxidation of amides (5.2). Oxidation of ethers to esters or lactones follows (5.3), then of sulfides to sulfoxides or sulfones (5.4) and of phosphines, arsine and stibines to their oxides (5.5). A final section (5.6) concerns such miscellaneous oxidations not covered by other sections in the book. 

Extensive studies on diastereoselectivity in the reactions of 1,3-dipoles such as nitrile oxides and nitrones have been carried out over the last 10 years. In contrast, very little work was done on the reactions of nitrile imines with chiral alkenes until the end of the 1990s and very few enantiomerically pure nitrile imines were generated. The greatest degree of selectivity so far has been achieved in cycloadditions to the Fischer chromium carbene complexes (201) to give, initially, the pyrazohne complexes 202 and 203 (111,112). These products proved to be rather unstable and were oxidized in situ with pyridine N-oxide to give predominantly the (4R,5S) product 204 in moderate yield (35-73%). 

This enzyme system catalyzes the oxidation of various nitrogen-, sulfur -, and phosphorus-containing compounds, which tend to be nucleophilic, although compounds with an anionic group are not substrates. For example, the N-oxidation of trimethylamine (Fig. 4.19) is catalyzed by this enzyme, but also the hydroxylation of secondary amines, imines, and arylamines and the oxidation of hydroxylamines and hydrazines ... 

N-oxidation. The oxidation of nitrogen in tertiary amines, amides, imines, hydrazines, and heterocyclic rings may be catalyzed by microsomal enzymes or by other enzymes (see below). Thus the oxidation of trimethylamine to anN-oxide (Fig. 4.19) is catalyzed by the microsomal FAD-containing mono oxygenase. The N-oxide so formed may undergo enzyme-catalyzed decomposition to a secondary amine and aldehyde. This N to C transoxygenation is mediated by cytochromes P-450. The N-oxidation of 3-methylpyridine, however, is catalyzed by cytochromes P-450. This reaction may be involved in the toxicity of the analogue,... 

Heteroaromatic N-Imines H.-J. Timpe, Adv. Heterocycl. Chem., 1974,17, 213-255. Chemistry of the Heterocyclic N-Oxides , A. R. Katritzky and J. M. Lagowski, Academic Press, New York, 1971. 

A nonbonding electron pair at the coupling nitrogen located in the plane of the a-CH bond of an imine makes up a positive contribution to JCN. This is recognized when comparing JCN of pyridine with the data of its cation and its N-oxide [135],... 

Clearly different ligand types will favor different oxidation states. Higher oxidation states prefer hard acid donor atoms, generally first-row p-block elements, rich in electron density and capable of strong a donation. A further provision is that they should resist oxidation. Common donor chromophores which have been used are amines N, imides (including oximes and imines)I>N , oxides —0 and fluorides F-. Second- and third-row p-block donors have also been used, forming bonds which are more covalent in character and creating special problems, as discussed below. 

The thiosemicarbazone of the 2-aldehyde (46) was studied by voltammetry, and the imine bond was found to be electroactive.67 Neither the 2- nor the 4-aldehyde N-oxide [2-(47) and 4-(47)] was reduced as expected, rather the aldehyde and the N-oxide were reduced together.68 The 3-aldehyde N-oxide [3-(47)] was reduced normally, giving the carbinol N-oxide. 

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