Thiyl radicals addition reactions

Similar reaction with (64 X = H) yields (65 R = Me). Thiyl radical addition to geranyl acetate yields expected cyclic and acyclic adducts in proportions ranging... 

Alkenes were cleaved to aldehydes by 5 mol% of a (salen VCl complex in the presence of air and thiophenols in 58-95% yield. Other V(III) and V(IV) catalysts are similarly effective. The reaction involves an initial thiyl radical addition to the olefin and trapping by oxygen. The resulting peroxyl radical is in turn most likely transformed to an alkoxyl radical by the catalyst and undergoes -fragmentation to form the most stable radical [198]. 

The reaction of tert-butanethiol with 1,1 -bis(cyclopropyl)ethene (16) alforded an approximately 2 1 mixture of the isomeric l-(ter -butylsulfanyl)-2-cyclopropylpentenes(17 - -18). Thiyl radical addition was followed by j8-scission and a subsequent 1,5-hydrogen atom migration. 

Previous study [18] on oxidation of thiols by transition metal oxide(s) in the presence of olefins resulted in the formation of corresponding sulphides indicating a free radical addition reaction in which metal oxide acts as an initiator for the production of thiyl radicals(RS-). The disulphide is formed by the dimerization of thiyl radieals (RS )- Based on this, a mechanism for thiol oxidation by manganese nodule (Only oxides of Mn, Fe, Co and Cu in manganese nodule are responsible for oxidation of thiols) is delineated as follows ... 

It also appears that intramolecular thiyl radical addition is a very efficient process compared to other free radical cyclizations. But competitive reactions such as polymerization are sometimes very difficult to suppress. Furthermore, other easy cyclization pathways, such as ionic ones, may complicate the interpretation of the results. Dronov s work exemplifies this possibility. Under all the experimental conditions used, l-pentene-5-thiol led to a Cy5/Cy6 mixture of products, with the (Cy5) compound being favored in sulfuric-acid-promoted cyclization and the (Cy6) compound being favored in photolysis. Thus the claim to have observed a homolytic reaction in cyclizations of ethylenic thiols generated from fatty acids, under conditions which did not avoid acid treatment, must be considered with care. 

TEP involves a stoichiometric reaction of a multifunctional olefin and a multifunctional thiol (e.g. thiol-vinyl ether, thiol-allyl ether, thiol-acrylate and thiol-yne). The reaction is a step-growth addition of the thiol to the double bond [1.46a]-[ 1.46c] formation of a thiyl radical, addition of the thiyl to the ene structure, regeneration of a thiyl, etc. termination occurs through recombination and disproportionation reactions. 

One further aspect apart from H-atom abstraction must be considered in the reactions of thiyl radicals with PUFAs, namely, the possibility of concurrent RS additions to the double bonds. By analyzing a particular system in which the thiyl radical from mercaptoethanol had reacted with linolenic acid, Schoneich et al. [56] came to the conclusion that the abstraction of bisallylic hydrogen and thiyl addition occur at comparable rates. The C-centered adduct radical formed in the addition reaction (27) is prone for repair in the presence of thiols, that is, it will subsequently regenerate thiyl radicals via reaction (1). These, in turn, will re-enter into the abstraction/addition competition cycle and eventually all of the thiyl radicals will appear to have reacted via the abstraction route. Experimentally, overall efficiencies of up to 85% have been measured. The difference from the limiting 100% efficiency is accounted for by side and termination processes. 

Formation of the (RSSR) radical cations can be achieved by oxidation of disulfides with OH radicals [157, 158]. As already indicated in Section 1.1 on thiyl radicals, this reaction enters into at least two different pathways. In the case of simple aliphatic disulfides the yields of (RSSR) amount to about 50% but appear to drop for more functionalized disulfides such as cysteine, cysteamine, and others. First, these lower yields may not be the true yields since buffer effects could have distorted the time-resolved conductivity signals by which these yields have been determined. But more importantly, additional reaction pathways may be entered. For several of these compounds weak absorptions at 374 nm have been observed indicating the possible formation of perthiyl radicals [159]. This is corroborated by the fact that the decay of this presumed RSS absorption is not accelerated by OH" addition as is the case for the (RSSR) band. 

Miyata O, Ozawa Y, Ninomiya I, Naito T. An enantioselective s3mthesis of (—)-a-kainic acid via thiyl radical addition-cycUzation-elimination reaction. Synlett 1997 (3) 275 276. 

The results were interpreted on the basis of a mechanism that starts with the photolytic formation of a radical cage consisting of an aryldiazenyl and and arylthiyl (Ar - S ) radical, followed by diffusion of both radicals out of the cage. Three reactions of the aryldiazenyl radical are assumed to occur bimolecular formation of the azoarene and N2, or of biphenyl and N2 (Scheme 8-37), the monomolecular dediazoniation (Scheme 8-38), and recombination with the thiyl radical accompanied by dediazoniation (Scheme 8-39). In addition, two radicals can react to form a di-phenyldisulfide (Scheme 8-40). 

In an analogous process, the reactions of unsubstituted and 2-substituted allyl phenyl sulfides with (TMSlsSiH give a facile entry to allyl fns(trimethylsilyl) silanes in high yields (Reaction 26). In this case, the addition of (TMSlsSi radical to the double bond is followed by the S-scission with ejection of a thiyl radical, thus affording the transposed double bond. Hydrogen abstraction from (TMSlsSiH by PhS radical completes the cycle of these chain reactions. ... 

The reaction of P-CAR with thiyl (RS ) and thiyl sulfonyl (RS()2 ) radicals have both been reported using pulse radiolysis (Everett et al. 1995, 1996). It was found that radical addition to P-CAR occurred and that p-CAR scavenges the thiyl radical, including that derived from glutathione, only via this mechanism, whereas it reacts with thiyl sulfonyl radicals by electron transfer as well. 

A review has been published on the methods of functionalization of tetrazoles for the period 2001 to mid 2005 <06RJOC469>. The search for new radical structures having both low selectivity and high reactivity toward the addition reaction onto alkenes has led to a new tetrazole-derived thiyl radical <06JOC9723>. 

Autoxidation of mercaptans gives rise to thiyl radicals, but these, like phenoxy radicals, are inert toward oxygen and normally dimerize to disulfides. Their participation in a chain reaction can be achieved in the co-oxidation of olefins and mercaptans, first demonstrated by Khar-asch (12), which takes advantage of the rapid addition of thiyl radicals to double bonds. 

In a similar manner, many additions of heteroatom radicals to unsaturated positions have been studied. In many cases, addition reactions of heteroatom radicals to alkenes are reversible and thermodynamically disfavored, but their occurrence is apparent. For example, the rapid addition and elimination of thiyl radicals to unsaturated fatty acid methyl esters results in isomerization reactions from which kinetic parameters can be obtained. Additions of group 14 (IV A) metal-centered... 

This reaction is based on a stoichiometric reaction of multifunctional olefins (enes) with thiols. The addition reaction can be initiated thermally, pho-tochemically, and by electron beam and radical or ionic mechanism. Thiyl radicals can be generated by the reaction of an excited carbonyl compound (usually in its triplet state) with a thiol or via radicals, such as benzoyl radicals from a type I photoinitiator, reacting with the thiol. The thiyl radicals add to olefins, and this is the basis of the polymerization process. The addition of a dithiol to a diolefin yields linear polymer, higher-functionality thiols and alkenes form cross-linked systems. 

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