Complexed amino radicals

Fujita S, Steenken S (1981) Pattern ofOFI radical addition to uracil and methyl-and carboxyl-substituted uracils. Electron transfer ofOFI adducts with N,N, Ar, Ar -tetramethyl-p-phenylenediamine and tetranitromethane. J Am Chem Soc 103 2540-2545 Fujita S, Nagata Y, Dohmaru T (1988) Radicals produced by the reactions of SO4 with uridine and its derivatives. Studies by pulse radiolysis and y-radiolysis. Int J Radiat Biol 54 417-427 Fujita S, Horii FI,Taniguchi R, Lakshmi S, Renganathan R (1996) Pulse radiolytic investigations on the reaction of the 6-yl radicals of the uracils with Cu(ll)-amino acid complexes. Radiat Phys Chem 48 643-649... 

Neutral aminyl radicals (I), also referred to as amino radicals, can be considered to be nucleophilic species whereas aminium cation radicals (II), metal complexed aminyl radicals (III), and amidyl radicals (IV) are electrophilic in nature. Greater utility has been observed with electrophilic nitrogen radicals than with neutral aminyl radicals (71 SI). Aminyl radicals are easily protonated with Br0nsted acids to give aminium cation radicals and readily complex with Lewis acids to form radicals III therefore, control of the reaction conditions is critical to ensure that reactions of interest are occurring from only one species. 

When metal ion complexed amino radicals are produced by the reaction of A -chloro amines with reducing metal salts in the presence of alkenes, /6-halo amines are produced12-39 41. The reaction of 1-chloropiperidine with cyclohexene, iron(II) sulfate and iron(III) chloride in methanol afforded mainly the d.s-adduct of 2. The diastereoselectivity is attributed to coordination of the unprotonated amino group with the iron(III) salt, which is mainly responsible for the chlorine atom transfer. With A-chlorodimethylarnine and 4-chloromorpholine lower yields are obtained. 

Lu C, Yao S, Lin N. (2001) Studies on reactions of oxidizing sulfur-sulfur three-electron-bond complexes and reducing a-amino radicals derived from OH... 

The decomposition reactions of amines are potential sources of the amino radicals. However, the reactions are complex and relatively little understood processes, and in most cases even the nature of the primary step is open to question. Quantitative studies are scarce. 

Thus, the types of reactions favored by amino radicals depend to a significant degree upon the extent with which the lone electron pair is associated with a proton, with a Lewis acid, or with an electron-withdrawing group. Clearly, aminium radical cations 2 (Scheme 1), metal-complexed aminyl radicals 3, amidyl radicals 4, sulfo-namidyl radicals 5 and cyanamidyl radicals 6 are electrophilic in nature. On the other hand, dialkylaminyl radicals 1 have been shown to display nucleophilic character... 

Complexed Amino Radicals. Since protonated amino radicals perform so well in addition reactions it Is not altogether surprising that metal complexed amino radicals also add well to unsaturated substrates. This area of amino radical chemistry has been studied by Minisci and his co-workers (18-21). 

The protonated amino radicals give a mixture of cis and trans products. The stereoselectivity of the complexed radical is presumably due to the intramolecular transfer of the chlorine atom. 

The product crystallized out of the reaction mixture as the zinc chloride complex. The state of the dimethylamino radical shown in brackets in the last equation is uncertain. It may or may not be coordinated with zinc chloride or it may originate from an S 2 displacement by styryl radical on the TMT ZnCl2 complex. Curiously no dimerization or disproportionation of the 8-amino-styryl radical was observed. Perhaps the coordination by zinc chloride prevents other reactions from occurring, allowing the combination with the second amino radical to occur reasonably efficiently. The reaction works well only with conjugated alkenes. Only slight reactions were observed with olefins such as 1-octene. 

The addition reactions of the zinc chloride-complexed amino radicals, described above were carried out in the absence of 0) gen. When oxygen was bubbled through the reaction mixture, the products were not the corresponding diamines but rather amino alcohols were isolated (27). Thus with styrene and a-methylstyrene, the reaction proceeded in the following fashion. 

In the a-alkylation of aldehydes, initiation of the photocatalytic cycle relies on sacrificial oxidation of the electron-rich substrate-enamine (or, eventually, arene)-and a reductive electron transfer to the a-bromocarbonyl substrate rapidly furnish the electron-deficient alkyl radical while returning Ru(bipy)3 to the catalytic cycle (Scheme 39.18). The electrophihc radical then adds to the generated chiral enamine formed by a parallel aminocatalytic cycle. The thus-formed electron-rich a-amino radical is oxidized by the Ru complex to produce the iminium ion and regenerate the active reductant, Ru(bipy)3 -a step that closes the photoredox... 

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