Radical donor

Irradiation of the A-bromo- or N- chloro-azetidin-2-ones (71) in the presence of alkenes, alkynes or radical donors induces rearrangement to the /3-haloalkyl isocyanates (72) via a... 

In their studies, Takasu, Ihara and coworkers used a new methodology based on a boomerang-type radical domino sequence [51], in which an iodoalkenyl can act as both radical donor and acceptor providing [4+2] or [4+1] cyclization products [52]. 

Homogeneous Processes with Tris-phenanthroline Metal(III) Oxidants. The rates of electron transfer for the oxidation of these organometal and alkyl radical donors (hereafter designated generically as RM and R, respectively, for convenience) by a series of tris-phenanthroline complexes ML33+ of iron(III), ruthe-nium(III), and osmium(III) will be considered initially, since they have been previously established by Sutin and others as outer-sphere oxidants (5). 

For the route A, acyl radicals donors like iS are readily generated from acyl selenides (ISa) or acyl cobalt derivatives (iSb) and radicals acceptors 2S are usually multiple bonds as in methyl vinyl ketone (2Sa) -although some homolytic substitutions are possible. On the other hand, nitriles GSal are useful acceptors (3S) in radical cyclisations and 4Sa is an obvious synthon equivalent of radical donor 4S (See Table 7.2). 

TABLE 7.2. Equivalent synthons of radical donors and radical acceptors... 

Application of Laccase as a Radical Donor in Adhesives for Particle Boards. The properties of laccase with regard to lignin render it a candidate for application in technical processes. A two-component adhesive was formulated with lignin as the phenolic component and laccase as radical donor. The process is described in more detail elsewhere (1). 

Trimethyl vinyl silane [754-05-2] M 100.2, 54.4 /744mm, 55.5°/767mm, d 0.6865, n 1.3880. If the H NMR spectrum shows impurities then dissolve in Et20, wash with aq NH4CI soln, dry over CaCl2, filter, evaporate and distil at atmospheric pressure in an inert atmosphere. It is used as a copolymer and may polymerise in the presence of a free radical donor. It is soluble in CH2CI2. [JOC 17 1379 7952]. 

The use of complex radical donors and radical acceptors, such as carbohydrates tethered by an acetal-containing linkage, has been reported by Sinay [98]. Here, the radical addition of an anomeric radical to a 4-exo-methylene sugar derivative (compound 69) proceeds in the 8-endo mode, with formation of a eight-membered acetal ring. The end product of this reaction, after removal of the tether and acetylation, is the C-disaccharide 70 (Scheme 27). 

Shock initiation has been studied in the presence of free-radical donors and getters (Ref 154). Detonation occurs only under particular vibration parameters (Ref 155). A new ACP (Augmented by Collision Pressure) method is said to be simpler and more reliable than conventional initiation procedures (Ref 105)... 

The hyperfine information for the series of azine radical donors requires deeper consideration. Gilbert et al. report detailed hyperfine information for unmethylated azine donors.However, the methylated donors provide a better model for application to the DCA species under consideration. Also, the Gilbert studies do not conclusively explain the experimental EPR data, noting a trend of reduced EPR resolution with donor heteroatom size, without conclusive explanation. We therefore have conducted a detailed study of the cw EPR for the oxidized methyl azine radical cation series (MePOZ , MePTZ" " , and MePSeZ ). 

Although silyl compounds have been thus employed in photochemical reactions as all l radical donors, sufficient levels of yields are attained only in quite limited cases. As the caibon-tin bond of cation radicals of stannyl compounds cleaves quite smoothly compared with the corresponding silyl derivatives in oxidation reactions with metallic reagents (see earlier section a-All lthioalkyl Cations from a-Stannyl Sulfides ), we examined the photochemical coupling reaction using organostannyl compounds. 

Rather than using the halogens themselves, other halo n radical donors are more commonly used in laboratory scale synthesis. One of the simplest of these is CCU, which can chlorinate alkanes by a free radical chain mechanism.The chain lengths are not very long (equations 76-78), because of their slightly endothermic nature and in part because the reaction is also kinetically rather slow. Elevated temperatures are therefore normally required. Nitrosylchloride at 1(X) C has also been used for these reactions. ... 

The antioxidant activity of individual tea polyphenols in different model assays showed a proportional relationship to the number of hydrogen radical donors of catechins. A synergistic effect was observed between tea catechins and caffeine, ascorbic, citric, malic, and tartaric acids and tocopherols (153). Formation of oxidation products of (+)-catechin dirring the antioxidative process has been observed in oxidation model studies. According to the proposed mechanism, (+)-catechin can scavenge four radicals per molecule (154, 155). Yamamoto et al. (156) have summarized the chemistry and application aspects of green tea, especially in relation to using their catechins. 

In this reaction example, the cracking products of polypropylene were used as methyl radical donors. 

Physical properties indicate that the dipolar contribution (1) is the major one and this structure actually accounts for the nucleophilic behavior of the terminal carbon of isonitriles. However, in terms of radical chemistry, the more interesting form is the divalent one (2). This clearly shows that the isonitrile group does not behave toward radical species like a vicinal radical acceptor/radical donor synthon, that is, like an usual unsaturated bond. It instead reacts like a geminal acceptor/donor synthon [2], where an incoming radical attacks the same carbon atom that will be the new radical center in the resulting imidoyl intermediate 3 (Scheme 1). Actually, isonitriles can serve as very efficient radical traps and this chapter reviews the structural, mechanistic, and synthetic studies carried out in this field, with outstanding results, in the last three decades. 

The general synthetic utility of the intermolecular addition of glycosyl-1-yl radical donors to electron-deficient alkenes for the synthesis of C-glycosides has been... 

Stereoselective addition of ribofuranosyl radicals to a, 9-unsaturated carbonyl compounds was exploited by Araki [22] in the formal synthesis of the antiobiotic Showdomycin 16 (Scheme 4). Barton [23] provided a more direct synthesis of 16 by addition of the ribofuranosyl radical, generated using the sugar telluride 17, to maleimide. Ribofuranosyl radicals also undergo addition to Tt-systems of electron-deficient aromatics such as 18, which provides a direct route to C-nucleosides [24], Addition of glycosyl radical donors to allyltributyltin was introduced by Keck... 

C-Glycosides are also prepared by the coupling of exocyclic carbohydrate-based radical donors with electron-deficient alkenes. Addition of the exocyclic radical derived from iodide 28 to the enone 29 led to the C-disaccharide 30 [34]. Motherwell [35] has shown that difluoromethylene-linked C-glycosides may be prepared by intermolecular additions of radicals derived from exocyclic difluorosulfides or sele-... 

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