Thiophenol, radicals from

Isotope maxima in radical reactions. Although hydrogen-atom transfer reactions are not of direct concern here, most interpretations of isotope effects strictly apply to hydrogen-atom rather than to proton transfers, and it is important to know whether the two types of reactions show the same experimental behaviour. It is thus of interest that a good example of a maximum has been observed by Pryor and Kneipp [78] for hydrogen abstraction by alkyl and aryl radicals from thiols and thiophenols (equation 41) ... 

Among the most useful radical fragmentation reactions from a synthetic point of view are decarboxylations and fragmentations of alkoxyl radicals. The use of (V-hydroxy-2-thiopyridine esters for decarboxylation is quite general. Several procedures and reagents are available for preparation of the esters,353 and the reaction conditions are compatible with many functional groups.354 f-Butyl mercaptan and thiophenol can serve as hydrogen atom donors. 

Szeimies recently published an impressive example of a steric effect on a Sr2 reaction at carbon for the addition of thiols to the central bond of bicyclo[ 1.1.0]-systems87. From the radical chain addition of thiophenol to 32 the stereoisomeric cyclobutanes 33a and 33b are obtained exclusively in 56% yield. The thiylradical... 

These reactions produce free radicals, as follows from the fact of consumption of free radical acceptor [42]. The oxidation of ethylbenzene in the presence of thiophenol is accompanied by CL induced by peroxyl radicals of ethylbenzene [43]. Dilauryl dithiopropionate induces the pro-oxidative effect in the oxidation of cumene in the presence of cumyl hydroperoxide [44] provided that the latter is added at a sufficiently high proportion ([sulfide]/[ROOH] > 2). By analogy with similar systems, it can be suggested that sulfide should react with ROOH both heterolytically (the major reaction) and homolytically producing free radicals. When dilauryl dithiopropionate reacts with cumyl hydroperoxide in chlorobenzene, the rate constants of these reactions (molecular m and homolytic i) in chlorobenzene are [42]... 

Homolytic hydrostannation can also be initiated at room temperature by thiophenols, when a trace of oxygen may oxidize the thiol to the ArS radical, which abstracts hydrogen from the stannane to give the stannyl radical (Equation (15)).93 With azoisobutyronitrile (AIBN) initiation, alkynes undergo only monohydrostannation, but with the thiol, simple alkynes show bis(hydrostannation) or bis(stannation). 

Irradiation accelerates the reactions of Scheme 4.1, and the substitution products are formed in 70-80% yields. Acceptors of radicals (e.g., di-tert-butylnitroxyl) or electrons (e.g., m-dinitro-benzene [DNB]) completely inhibit the snbstitution even if the acceptors are added to the reaction mixture in small amonnts. The mentioned snbstitution reactions do not take place when no cyano groups are present in the initial a-phenylsnlphonyl cumene. Hence, the cyano groups send the reaction via the ion-radical pathway. Like the nitro gronp, the cyano group promotes the formation of anion-radical, which originates on one-electron transfer from the thiophenolate or malonate ions to the substrate. 

The reaction in Scheme 5.2 proceeds through the formation of the 1-bromonaphthalene anion-radical, which rapidly converts into the naphthyl radical. Thiophenolate intercepts the naphthyl radical and forms the anion-radical of l-(phenylthio)naphthalene. The reaction takes place in the preelectrode space. It competes with the formation of the unsubstituted naphthalene. The debromi-nation is a result of hydrogen abstraction from the solvent SolH by the naphthyl radical. The unreacted 1-bromonapthalene oxidizes the l-(phenylthio)naphthalene anion-radical formed. This leads to the neutral l-(phenylthio)naphthalene and the anion-radical of 1-bromonaphthalene. The reaction takes place in the bulk solution and is the key-point for the chain propagation. 

Swartz and Stenzel (1984) proposed an approach to widen the applicability of the cathode initiation of the nucleophilic substitution, by using a catalyst to facilitate one-electron transfer. Thus, in the presence of PhCN, the cathode-initiated reaction between PhBr and Bu4NSPh leads to diphe-nydisulfide in such a manner that the yield increases from 10 to 70%. Benzonitrile captures an electron and diffuses into the pool where it meets bromobenzene. The latter is converted into the anion-radical. The next reaction consists of the generation of the phenyl radical, with the elimination of the bromide ion. Since generation of the phenyl radical takes place far from the electrode, this radical is attacked with the anion of thiophenol faster than it is reduced to the phenyl anion. As a result, instead of debromination, substitution develops in its chain variant. In other words, the problem is to choose a catalyst such that it would be reduced more easily than a substrate. Of course, the catalyst anion-radical should not decay spontaneously in a solution. 

Consumption of the DSBPD results from further oxidation of the >NO radical (Reaction 12) but may also occur by hydrogen abstraction from the alkyl group leading to imine formation (5) or by disproportionation reactions yielding quinonoid structures (9). The existence of this reaction system may therefore be transitory. However, the main chain is long, and the effect of 7.5 X 10"3M DSBPD lasts almost throughout the oxidation of 0.15M indene-thiophenol (see Figure 3). 

Christen247 has found that 1 reacts with thiols and tri- and tetrahalomethanes under radical conditions to give products with the opposite orientation to that expected from reaction with an electrophile. Equation 30 depicts two such processes. In similar vein, 11 has been shown to interact with thiophenol and tributyltin hydride to give 3-substituted 2-methyl-... 

The derived hydroxy-aldehyde was selectively oxidised via its cyanohydrin derivative to the corresponding hydroxy-methyl ester 9. Thinyl radical, generated photolytically from thiophenol, attacked, due to steric reason, regioselectively the terminus of the arylacetylene unit... 

Aryl radicals electrochemically generated from the cleavage of aryl halide radical anions have been observed to react with nucleophiles other than iodide (Pinson and Saveant, 1974, 1978 Saveant, 1980), a reaction known as the SrjjI reaction (Bunnett, 1978). The most commonly used nucleophiles are thiophenolate, mercaptides, and cyanide ion. The reactions observed are... 

The author s group [12] tried to find saturation behavior of the MFEs due to the AgM in fluid solutions with our pulsed magnet and found that the MFEs on the escape radical yield (1e(B)) observed for the photoreduction of 4-methoxybenzophenone with thiophenol (Reaction S-5 in Table 7-2) were almost saturated by the fields of -30 T. The isotropic g-values of the thiyl and ketyl radicals have been determined to 2.0082 and 2.0027 so Ag=0.0055 [12]. From ns-laser photolysis measurements with our electromagnet, superconducting magnet, and pulsed magnet, we observed the time profiles of the transient absorption (A(f) curves) of the ketyl radical and obtained the MFEs (A(B)=Ye(B)/1e(0 T)) on the )4eld. The R(B) values obtained at room temperature in 2-methyl-1-propanol are plotted... 

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