Diaziridine oxidation

In the diaziridine field many compounds are known bearing N-YL, A/-alkyl and A-acyl groups, but here no dramatic changes in reactivity are caused by A-substituents. N-Aryldiaziridines are underrepresented. The ring carbon is in the oxidation state of a carbonyl compound or, in the diaziridinones (5) and the diaziridinimines (6) that of carbonic acid. In single cases, diaziridine carbon bears chlorine or fluorine. 

Diaziridines, discovered in 1958, six years after the oxaziridines, were almost immediately realized to be structural analogs of oxaziridines. Like these they showed oxidizing properties unexpected for other classes of organic nitrogen compound. Properties in common with oxaziridines include the rearrangement to open chain isomers on heating above 100 °C (for several diaziridines), and their hydrolytic behavior in acidic media, which leads to carbonyl compounds with conservation of the hetero-hetero bond. 

The diaziridine ring exhibits a surprising stability towards strong oxidizing agents. Diaziridines unsubstituted at both N atoms can be transformed into diazirines by dichromate in acidic solution or by chlorine (Section 5.08.4.3). Radical attack by decomposing peroxide converts (136) to the diaziridinyl radical (137), as evidenced by ESR spectroscopy (76TL4205). 

Clean examples of diaziridine to hydrazone rearrangements are rare. Diaziridine (119) mentioned above rearranges to the isomeric enhydrazone in boiling toluene, and 2,4-dinitrophenyldiaziridine (125) under the same conditions affords the 2,4-dinitrophenylhy-drazone (145) within 4 h. On blocking this rearrangement by iV-methyl, conversion with loss of cyclohexanone occurred to give benzotriazole iV-oxide (146) (72JOC2980). 

Diaziridines are also very strong oxidizing agents, even liberating chlorine from hydrochloric acid. The reaction with iodide in acidic solution proceeds almost quantitatively in most cases. The two equivalents of iodine obtained from a diaziridine (151) are of analytical value together with the number of acid equivalents consumed (B-67MI50800). 

It was not their reactivity but their chemical inertness that was the true surprise when diazirines were discovered in 1960. Thus they are in marked contrast to the known linear diazo compounds which are characterized by the multiplicity of their reactions. For example, cycloadditions were never observed with the diazirines. Especially surprising is the inertness of diazirines towards electrophiles. Strong oxidants used in their synthesis like dichromate, bromine, chlorine or hypochlorite are without action on diazirines. Diazirine formation may even proceed by oxidative dealkylation of a diaziridine nitrogen in (186) without destruction of the diazirine ring (75ZOR2221). The diazirine ring is inert towards ozone simple diazirines are decomposed only by more than 80% sulfuric acid (B-67MI50800). 

Most diazirines are easily obtained from diaziridines. Dialkyldiazirines are simply formed by dehydrogenation of 3,3-dialkyldiaziridines (60AG781). For example, the spirodiazirine (187) can be prepared in 65-75% yield from the diaziridine with silver oxide (6508(45)83). 

The parent compound, cyclic diazomethane , was first obtained from formaldehyde, ammonia and chloramine by dichromate oxidation of the initially formed higher molecular diaziridine-formaldehyde condensation product (61TL612). Further syntheses of (44) started from Schiff bases of formaldehyde, which were treated with either difluoramine or dichloramine to give (44) in a one-pot procedure. Dealkylation of nitrogen in the transient diaziridine was involved (65JOC2108). 

The discussion of the structure of the nitrones and the hydrazones received less attention. With the increased application of physical methods to structural problems, the three-membered ring structures for these compounds lost much of their attraction. The problem of the structure of the nitrones was satisfactorily solved with the open-chain A -oxide formulation. The compounds originally designated as diaziridines (2) were partly reformulated with the open-chain hydra-zone structures and partly were left without a. satisfactory proof of structure. 

Methyldiaziridine and 3-n-propyldiaziridine (45) give with benzoyl chloride the dibenzoyl compounds 48 and 49. Both compounds are shown to be true diaziridines by oxidizing iodide. This discovery was of special interest the sole compounds retained in recent literature- of those formerly formulated as diaziridines were supposedly 1,2-diacyl-diaziridines, e.g. 50 [compare Section I, Eq. (1)]. 

These compounds, however, show no oxidizing power. Their diaziridine structure is thus erroneous. ... 

Trialkyl-diaziridines (e.g. 51) react with phenyl isocyanate with the same ease as the 1,3-dialkyl analogs. However, the compounds which result from the components in ratio 1 1 are not oxidizing agents and thus are not diaziridines. ... 

Finally, the oxidative action of diaziridines toward hydrogen sulfide... 

Dialkyl-diaziridines (35) possess a considerable reducing pow er they are dehydrogenated by yellow mercuric oxide or alkaline perm s. R. Paulsen, Angcw. Chern. 72, 781 (1960). 

For the preparation of the parent substance, cyclic diazomethane (67), formaldehyde, chloramine, and ammonia were reacted. Diaziri-dine formation was successful in about 20% yield the diaziridine condensed with further formaldehyde to high molecular weight products the diaziridine detected by its oxidizing power was nonvolatile. Oxidation with dichromate in dilute sulfuric acid led to gaseous diazirine (67) [Eq. (56)]. It was only investigated in solution. 

The reaction of hexafluoroacetone azine with cycloheptatriene at 70 °C provides after 8 days a mixture containing 28% of unchanged azine 290 and products formed by three distinct mechanistic pathways, that is, criss-cross cycloaddition product 294, a bis-ene adduct 295 and its oxidation product 296, and [3+6] cycloaddition leading to diaziridine 297, in the ratio 15 38 7 (Scheme 40) <1995JFC(73)203>. 

The nickel hydroxide electrode is well suited for the oxidation of diaziridines (55) to diazirines (56) (Eq. (16), Table 18). The low isolated yield for 56b compared to its high glc-yield is due to the volatility of the diazirine. The yields compare favorably with those found with silver oxide, the best chemical oxidant reported for this conversion. 

Table 18. Oxidation of diaziridines (55) to diazirines (56) at the nickel hydroxide electrode...

The 1,7-electrocyclization of azomethine imines 106 and 109, with an a,13-aromatic bond and the N—O bond of a nitro group as the y,8-bond, has been proposed as a key step in the conversion of azomethine imines 106 (Scheme 33) [62AG(E)158] or diaziridines 108 (Scheme 34) to benzotri-azole- 1-oxides 107 and 110, respectively (72JOC2980). 

Fluoroalkylatcd diazirines are an interesting class of compounds that are prepared from the corresponding diaziridincs. Thus, the oxidation of 3-aryl-3-(lrifluoromethyl)diaziridine (t) to diazirine 2 is carried out with a mixture of dimethyl sulfoxide/oxalyl chloride in good yields.256 This gentle oxidation does not affect the sulfur in 2-thienyl aziridines. Similarly, the oxidation of diaziridine 3 to bis(Lrifluoromethyl)diazirine 4 is accomplished using lead(IV) acetate.244 This diazirine can be stored in a steel cylinder at 25r C and shows no tendency to detonate. 

Dehydrogenation of diaziridines.2 The Swern reagent is more effective than Ag20 or NBS for oxidation of the diaziridines 1 to the diazirines 2, of interest because they are photolyzed to reactive carbenes. 

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