Pyrroline N-oxide

Pyrroline-N-oxides (12) are sometimes isolated when using zinc-ammonium chloride (19,20), iron-sulfuric acid (14) or hydrazine-Raney nickel (21) as reducing agents. During the reduction, dimerization has been often observed (22). 

A -Piperideine-N-oxide was obtained along with a dimeric product by oxidation of N-hydroxypiperidines with mercuric acetate or potassium ferricyanide (107-109). 2l -Pyrroline-N-oxide is formed by oxidation of N-ethylpyrrolidine with hydrogen peroxide with simultaneous formation of ethylene (110). 

A -Pyrroline-N-oxides when unsubstituted in the 2 position readily add hydrogen cyanide. The 1 -hydroxy-2-cyanopyrrolidines thus formed undergo oxidation to 2-cyano-J -pyrroline-N-oxides. 

The dimer of 1-methyl- -pyrroline (39) was obtained by reduction of N-methylpyrrole with zinc and hydrochloric acid (132) and, together with the trimer, by mercuric acetate dehydrogenation of N-methylpyrrolidine (131). J -Pyrroline-N-oxides form dimers in a similar manner (302). Treatment of 1,2-dimethyl-zl -piperideine with formaldehyde, producing l-methyl-3-acetylpiperidine (603), serves as an example of a mixed aldol reaction (Scheme 18). 

In related work, the reactions of hydrogen peroxide with iron(II) complexes, including Feu(edta), were examined.3 Some experiments were carried out with added 5.5"-dimethyl-1-pyrroline-N-oxide (DMPO) as a trapping reagent fa so-called spin trap) for HO. These experiments were done to learn whether HO was truly as free as it is when generated photochemically. The hydroxyl radical adduct was indeed detected. but for some (not all) iron complexes evidence was obtained for an additional oxidizing intermediate, presumably an oxo-iron complex. 

Recendy, PEN, a-4-pyridyl-oxide-N-t-butyl nitrone (POEN) or 5-5,dimethyl-1, pyrroline-N-oxide (DMPO) were evaluated in models of experimental shock (endo-toxic, traumatic and mesenteric artery occlusion in rats). All three nitrones, when given prior to the insult intraperitoneally, were protective. When the nitrone s spin trapping ability was inactivated by exposure to solar light and air, they were no longer efficacious (Novelli, 1992). 

Fig. 3. Preferred TS trajectory for the cycloaddition of 5-substituted pyrroline N-oxides to ring-substituted methylenecyclopropanes...

Photoisomerization of nonconjugated nitrones, in particular derivatives of 3-imidazoline-3-oxide and pyrroline-N -oxide, appears to be irreversible (Scheme 2.83) (10, 452). 

The stereocontrolled addition of TMSCN to chiral 3.4-dihydro-277 - pyrroline N - oxides (394) is being used to prepare enantiopure 2-aminomethylpyrrolidines (395) and (396) (Scheme 2.172) (631). 

The use of nitrone scavengers was precedented by the work of Iwamura and Inamoto (1967), who had used esr spectroscopy to detect the nitroxide formed by addition of cyanopropyl radicals to the cyclic nitrone, 5,5-dimethyl-pyrroline-N-oxide (DMPO) [2], and had actually isolated the cyanopropyl radical adduct of the nitrone [3]. 

As a means of identifying the potent oxidant another approach was made. By the use of certain organic compounds one can infer the presence of a free radical by converting a highly unstable one such as OH to a much more stable compound which can accumulate in solution, rendering its detection by electron spin resonance possible. To measure the presence of OH the compound DMPO (5,5-dimethyl l-pyrroline-N-oxide) has been used The characteristic adduct of OH with... 

Similarly, pyrroline N-oxides (12), pyrrolines, or pyrrolidines can be prepared from y-nitro ketones (13) in aqueous organic media at low temperatures the pyrroline N-oxide is obtained66 [Eq. (26)]. 

Perhydropyrrolo[l,2-fc]isoxazoles result from 1,3-dipolar cycloaddition of cyclic nitrones with alkenes. The high regio- and stereoselectivity of this cycloaddition has been used to control the stereochemistry in the synthesis of natural products. As one example, pyrroline N-oxide (70) and 3,4-dimethoxystyrene gave a diastereomeric mixture of pyrroloisoxazoles (71) and (72), in nearly quantitative yield with preferential formation of (71). 

Pyrrolinediones polymerization, 1, 273 2-Pyrroline-4,5-diones synthesis, 4, 143 3 -Pyrroline-2,5-diones polymers, 1, 294 Pyrrolines N-oxide... 

ESR (Electron Spin Resonance) spectrum (Fig. 1.2) recorded during electrolysis of DMPO (5.5 dimethyl-1-pyrroline-N-oxide) solution on BDD confirms the formation of OH during anodic polarization of diamond electrodes. It has been reported that the BDD-hydroxyl radical interaction is so weak (no free p or d orbitals on BDD) that the OH can even be considered as quasi-free. These quasi-ffee hydroxyl... 

The existence of free hydroxyl radicals in photo-initiated AOPs can be proven by applying a well-established method, the so-called spin trapping technique. The diamagnetic spin trap 5,5 -dimethyl-1-pyrroline N-oxide (DMPO) forms a stable paramagnetic spin-adduct with OH radicals. Its formation can be detected by electron paramagnetic resonance (EPR) spectroscopy. The underlying chemistry of... 

Deoxygenation of a nitrone. Some years ago Todd and co-workers noted that 1-pyrroline-1-oxides can be obtained by reductive cyclization of a y-nitro ketone. This reaction was used recently in a synthesis of chlonns related to vitamin B,. Thus the nitro ketone 1 on reduction with zinc and acetic acid gives the pyrroline N-oxide 2 in high yield. The N-oxide is stable to triphenylphosphiue or trimethyl phosphite, but is reduced to the imine 3 in high yield by TiCl,. 

C6H11CI 4-chloro-2-hexene 6734-98-1 396.15 34.967 1,2 8112 C6H11NO 5,5-dimethyl-1-pyrroline N-oxide 3317-61-1 474.25 41.416 2... 

A new nitrone, 5-methyl-5-phosphono-l-pyrroline N-oxide (DHPMPO), has... 

N-methylen-tert-butylamin-N-oxid 7991a> and 5,5-dime thyl-A1 -pyrrolin-N-oxid T892 have been employed as spin traps, but a variety of other nitrones is also suitable93. While ESR data from adducts to 81 c give relatively little information on fine structure of the radicals88, in the spectra of adducts from 79 and 78 more such information is recognizable926 d 94 ... 

A new spin-trap, 5-(diethoxyphosphorylmethyl)-5-methyl-4,5-dihydro-3H-pyrrole N-oxide (48), " and its hydroxyl- and superoxide-spin adducts, have been compared with the analogues obtained with 5-(diethoxyphosphoryl)-5-methyl-4,5-dihydro-3H-pyrrole N-oxide (49 DEPMPO) and with 5,5-dimethyl-1-pyrroline N-oxide (50 DMPO), and overall the spin trapping behaviour of 48 was found to be more similar to that of DMPO than DEPMPO. 

CuZnSOD has been demonstrated to act as a peroxidase, oxidizing various substrates, among them nitrite (to NO2) [57] and relatively bulky molecules such as 5,5-dimethyl- 1-pyrroline N-oxide (DMPO to DMPO-OH), tyrosine (to dityrosine) or 2,2 -azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS to a cation radical). However, the enzyme becomes inactivated in the presence of H2O2. Apparently, hydrogen peroxide reduces Cu- at the active site of the enzyme. Subsequent reaction of H2O2 with Cu generates a potent oxidant (Cu+-0 or Cu + CH) that can attack the adjacent histidine residue and thus inactivate the enzyme, or oxidize an alternative substrate [3]. Most authors assume that the mechanism of the peroxidative action of CuZnSOD, significantly accelerated in the presence of bicarbonate, consists in oxidation of bicarbonate to a carbonate radical anion able to oxidize other substrates [58,59] ... 

The conservation of the cis arrangement of two substituents during ring closure favors formation of bicyclic oxaziridines, which has been observed repeatedly, for example, in the illumination of pyrroline N-oxides 72 ° or the derivative 73 of a steroidal alkaloid. ... 

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