Diazirines, reduction

Reductions of the N —N double bond yield diaziridines and were carried out for proof of structure, using for example sodium amalgam or catalytic hydrogenation. They are unimportant beyond that, because most diazirine syntheses start with diaziridines. 

The action of strong reducing agents on diazirines leads to basic products. Diaziridines can be detected as intermediates in the reaction. The reduction of 3,3-diethyldiazirine to 3,3-diethyldiaziridine [Eq. (61)1 serves as a proof of structure of the diazirines. 

Because the diaziridines can easily be further reduced, their isolation from the reduction of the diazirines is only possible in poor... 

The electrochemistry of diazirines and diaziridines was discussed in Part I.1 Di-tert-butyldiaziridone (178) can be reduced in aprotic media in an irreversible two-electron reduction.275 Whereas diaziridines require acidic conditions for the splitting of the N—N bond and are electrochemically inert toward reduction in alkaline solutions, 178 is reduced in aprotic media to di-tert-butylurea [Eq. (108)]. 

In the case of diazirines, both difluorodiaztrine and bis(trifluoromethyl)diazirine have been obtained. Difluorodiazirine was originally prepared by reductive defluorination of bis(difluoroamino)difluoromethane [320, 321], but it can also be obtained by an interesting fluoride-ion-induced rearrangement of difluorocyanamide [322] (Figure 8.125). Bis(trifluoromethyl)diazirine [318, 323] is best obtained by the oxidation of 2,2-diaminohexafluoropropane, prepared from hexafluoroacetone, with sodium hypochlorite (Figure 8.126). 

The iV-diaziridinyl anion 33 has been generated from diazirine 32 in a Fourier transform mass spectrometer by reduction of the diazirine (Scheme 6). The acidity of its conjugate acid and the electron affinity of its corresponding radical were measured and used to calculate the N-H bond strength in /r J-diaziridine (88 4kcalmoP ) <1999IJM179>. 

The syntheses of diazirines and diaziridines are closely related due to the relative ease of interconversion between the species by reduction/oxidation <1996GHEC-II(1A)347>. Consequently, diazirines and diaziridines are both commonly synthesized by the well-established methods of Schmitz <1961CB2166> (Scheme 18) and Graham <1965JA4396> (Scheme 19), and these are described in previous editions <1984CHEC(7)195, 19%CHEC-II(1A)347>. 

An extension of the Graham method of diazirine synthesis has enabled the first synthesis of 3-carboalkoxy-3-halodiazirines (e.g., 76) <2004JOC7359>. Conversion of the amidines 74a and 74b into the corresponding N,N,N -trichloroamidines 75a and 75b was achieved through successive chlorination steps reductive dechlorination with bromide or chloride gave the diazirines 76a and 76b (Scheme 26). 

Diazirines are polarographically reducible in acid solution in a four-electron reduction to a g w7-diamine, which is hydrolyzed to a carbonyl compound, and in alkaline medium in a two-electron reaction [298] to a diaziridine. Diaziridines are reducible only in acid solution... 

The protonated diaziridine is more easily reducible than the diazirine, which has too weakly basic properties to be protonated in aqueous solution. In alkaline medium in which both are unprotonated, the diazirine is the more easily reducible. This explains why it has been difficult to obtain good yields of diaziridine by chemical and catalytic reduction of a diazirine if such a reduction is to result in a high yield of diaziridine, it must be performed in an alkaline medium. 

One may postulate that H atom transfer to excited-state diazirine 45 leads to a diazene, 3-diazenylnortricyclane, that is responsible for the reduction... 

Diazirines fluorinated at the ring carbon were first described by Mitsch, °° and shortly afterward by Rebertus and co-workers. They are obtained from suitable perfluorinated amines by reduction with ferrocene or iodide, as well as by reduction with diphenylamine, semicarbazide hydrochloride and by electrolytic reduction. ... 

Prepared by lead tetraacetate oxidation of the corresponding diaziridine, bis(trifluoromethyl)diazirine (263) has also been made by hypochlorite oxidation of hexafluoroacetone aminal 262. Instead of by oxidation, ring formation in the case of difluorodiazirine (265) has been achieved by mild reduction of bis(difluor-... 

Tetrathianes. (1) Oxidative dimerization of a,a-disuhstituted alkanedithioic acid dianions (Scheme 38) or 1,1-dithiols (Equation 17) - very limited examples and a-monosuhstituted alkanedithioic acids decompose (2) reductive or pyrolytic dimerization of gi OT-disulfenyl dichlorides (Equation 18) - only malonate-derived examples (3) reaction of a-chloro sulfenyl chlorides with sodium trithiocarhonate (Equation 19) - only malonate-derived examples (4) sodium thiophenoxide-catalyzed reaction of thioketones with elemental sulfur (5) reaction of benzo-furan-3(2//)-one with S2CI2" (6) UV irradiation of a CS2 solution of a diazirine (7) reaction of a 2,2,4-trisubstituted-1,3-dithietane with Oxone (Scheme 54)". Method (4) is the most convenient and general of these. 

A patent conconed with the preparation of fluorinated diazirines via the reductive cyclization of gem-bis(difluoroamino)-compounds has been published, and so have papers which refer to synthetic uses of perfluoro-... 

The electrochemical behaviour of diazirines has been described" Controlled potential electrolysis of (349 R=C1, Ar=CgH, 4-MeOCgH ) at vitreous carbon in MeCN at 10°C affords the corresponding nitriles ArCN(80-90j5) by irreversible 1 electron reduction. In contrast to this (349 R=r u, Ar=Ph) is reduced, in the presence of a proton source, to the corresponding aziridine. 

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