Induced Thermolysis of tert-Butyl Phenylperacetates by Thiophenol: Simultaneous Occurrence of Homolysis and Single Electron Transfer

Abstract

Thermolysis of tert-butyl phenylperacetates in the presence of thiophenol takes place via dual mechanism. The two-bond homolysis indicates rho(+)(4)= -1.16, testifying to polar transition states. The single electron transfer yields a radical anion intermediate which undergoes fragmentation with rho(ET) = 1.01.

Thermal decomposition of the tert-butyl perester of thymidine-5′-carboxylic acid. Formation and fate of the pseudo-C4′ radical

“…The acid 6 was probably formed by a SET process between perester 1 and PhSH, leading to a perester radical anion 1 z2 , from which 6 eventually arose by loss of tert-butoxy radicals (Scheme 4). Similar SET processes between peresters and the sulfur atom of sulfides 12 and thiols 13 have been already reported. The decomposition of 1 carried out in tert-butanol in the presence of a 5-fold excess of PhSH similarly gave the radical product 5 and the in cage product 4a together with minor amounts of thymine 3 and acid 6 ( Table 1, entry 4).…”

“…After prolonged heating (3 h), HPLC analysis showed the disappearance of the acetal 4a; thymine 3 and compound 5 were the major products, together with minor amounts of acid 6 ( Table 1, entries 8,9). The latter was most probably derived from 1 through SET reduction by GSH; 13 as expected, the yield of acid 6 increased with increasing the GSH concentration. These findings can be easily rationalized by assuming that the chemical behavior of perester 1 (and radical 2) in water/ tert-butanol is strictly related to that exhibited in neat tertbutanol and methanol.…”

Molecule‐Induced Radical Formation (MIRF) Reactions—A Reappraisal

“…This is particularly relevant for peroxides and peresters, whose O−O bond fragments can serve as one‐electron acceptors. An example is given in Scheme for the reaction of tert ‐butyl phenylperacetate ( 50 ) with thiophenol ( 51 ) . The proposed mechanism was tailored from earlier studies on reactions of neutral nucleophiles (such as sulfides, disulfides, and amines) with esters and anhydrides of peracids.…”

“…Experimental proof for MIRF reactions is sometimes difficult to obtain because of the numerous mechanistic alternatives leading from the same reactants to the same products.Aside from the above-mentioned competition with stepwise processes initiated by unimolecular OÀOb ond cleavage,M IRF reactions also compete with single electron transfer (SET) reactions between the two reaction components.This is particularly relevant for peroxides and peresters, whose O À Ob ond fragments can serve as one-electron acceptors.A ne xample is given in Scheme 5f or the reaction of tert-butyl phenylperacetate (50)w ith thiophenol (51). [52] Theproposed mechanism was tailored from earlier studies [53] on reactions of neutral nucleophiles (such as sulfides, disulfides,and amines) with esters and anhydrides of peracids. Theexample chosen here has the advantage that the stepwise and SET processes lead to slightly different products.T he stepwise mechanism (A)involves initial OÀObond homolysis in perester 50,f ollowed by (irreversible) decarboxylation of radical 52 to afford benzyl radical 24.T rapping all open-shell species by hydrogen abstraction from thiophenol generates tert-butyl alcohol (53), toluene (22), and diphenyldisulfide (54).…”

Molekül‐induzierte Radikalbildung – eine Neubewertung

“…Dies ist besonders bei Reaktionen von Peroxiden und Perestern relevant, deren O‐O‐Homolysefragmente auch als Einelektronenakzeptoren fungieren können. Ein Beispiel hierfür ist die Reaktion von tert ‐Butylphenylperessigsäure ( 50 ) mit Thiophenol ( 51 ) . Der hier vorgeschlagene Mechanismus leitet sich von früheren Untersuchungen zur Reaktion von Neutralnucleophilen (wie Sulfiden, Disulfiden und Aminen) mit Estern oder Anhydriden von Persäuren ab.…”