Electron transfer in the reaction of benzaldehyde with a nonstabilized ylide

Yamataka, Hiroshi; Nagareda, Katsushi; Hanafusa, Terukiyo; Nagase, Shigeru

doi:10.1016/s0040-4039(01)93930-9

Cited by 22 publications

(4 citation statements)

References 19 publications

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“…The one electron transfer mechanism was also advocated by Yamataka and co-workers on the basis of their observation that there is no significant kinetic isotope effect for the reaction of isopropylidenetriphenylphosphorane with benzaldehyde having a 14 C-labelled carbonyl group. 82 Evidence against this mechanism. A number of tests for radical involvement in Wittig reactions are described in the review of Vedejs and Peterson.…”

Section: Olah's Single Electron Transfer Mechanismmentioning

confidence: 99%

The modern interpretation of the Wittig reaction mechanism

2013

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Section: Olah's Single Electron Transfer Mechanismmentioning

confidence: 99%

The modern interpretation of the Wittig reaction mechanism

2013

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“…Here, isomerization of the starting cis enone to trans upon mixing with a reagent is taken as indication of occurrence of ET from the reagent to the enone. Since Z -2,2,6,6-tetramethylhept-4-en-3-one has more negative reduction potential (−2.28 V vs SCE) than benzaldehyde (−1.84 V) and benzophenone (−1.82 V), a positive response in the enone-isomerization experiment then indicates the possible occurrence of ET to the aromatic aldehyde and ketone. Dehalogenation experiment measures the occurrence of ET from a reagent to halobenzophenone .…”

Section: Resultsmentioning

confidence: 99%

Reactions of PhSCH₂Li and NCCH₂Li with Benzaldehyde and Benzophenone: When Does the Mechanism Change from ET to Polar?

et al. 2001

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The carbonyl-carbon kinetic isotope effect (KIE) and the substituent effect were measured for the reaction of phenylthiomethyllithium (PhSCH(2)Li, 1) with benzaldehyde and benzophenone, and cyanomethyllithium (NCCH(2)Li, 2) with benzaldehyde, and the results were compared with those for other lithium reagents such as MeLi, PhLi, CH(2)=CHCH(2)Li, and CH(2)=C(OLi)C(CH(3))(3). It was previously shown that the reactions of MeLi, PhLi, and CH(2)=CHCH(2)Li proceed via a rate-determining electron transfer (ET) process whereas the reaction of lithium pinacolone enolate goes through the polar (PL) mechanism. The reaction of 1 with benzaldehyde gave no carbonyl-carbon KIE ((12)k/(13)k = 0.999 +/- 0.004), similar to that measured previously for the MeLi reaction with benzophenone ((12)k/(14)k = 1.000). The effect of substituents of the aromatic ring of benzaldehyde and benzophenone on the reactivity gave very small Hammett rho values of 0.17 +/- 0.03 and 0.26 +/- 0.05, respectively. These small rho values are again similar to that observed for the reaction of MeLi. Likewise the reactions of 2 with benzaldehydes gave small KIE and the rho value ((12)k/(13)k = 0.996 +/- 0.004, rho = 0.14 +/- 0.02). Dehalogenation and enone-isomerization probe experiments for 2 showed no evidence for the presence of radical-ion pair of sufficient lifetime during the course of the reaction. It is concluded that the reactions of 1 and 2 with the aromatic carbonyl compounds proceed via the electron transfer-radical coupling mechanism with rate-determining ET as in the reactions of MeLi, PhLi, and CH(2)=CHCH(2)Li.

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“…The enone-isomerization probe is one of such criteria, and its usefulness has been proved in the literature. , Here, isomerization of the starting Z -enone ( Z - 5 ) to the E -enone ( E - 5 ) upon mixing with a reagent is taken as an indication of the occurrence of ET from the reagent to the enone (eq 4). Since the reduction potential of the Z -enone is more negative (−2.28 V vs SCE) than those of benzaldehyde (−1.84 V) and benzophenone (−1.82 V), a positive response of the enone-isomerization probe then indicates the possible occurrence of ET to the aromatic aldehyde and ketone. Table lists the results of enone-isomerization probe experiment of 3 , together with those of other ylides.…”

Section: Resultsmentioning

confidence: 99%

Detection and Reaction of Oxaphosphetanes Derived from Benzaldehyde and 1-Adamantylmethylidene Ylide

1996

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The Wittig reaction of (1-adamantylmethylidene)triphenylphosphorane (Ph(3)P=CH(1-Ad)) with benzaldehyde was investigated, and the results were compared with those of other ylides. The substituent effect in the reaction of the ylide with benzaldehydes was determined by competition experiments, which gave a Hammett rho value of 3.2. The rho value is much larger than those reported for analogous reactions of Ph(3)P=CH(CH(2))(2)CH(3) (rho = 0.20) and Ph(3)P=CH(CH(3))(2) (rho = 0.59), indicating that the reaction mechanism differs for Ph(3)P=CH(1-Ad) and the other ylides. The cis/trans ratio of the product alkene is 74/26 for the reaction with the parent benzaldehyde and highly depends on the position of the substituent; ortho substituted benzaldehydes gave the trans alkenes up to 90%. Monitoring the reaction by means of (31)P NMR revealed that both cis and trans oxaphosphetane intermediates were formed and that the formation and decomposition of the cis oxaphosphetane are 7-12 times faster than those of the trans oxaphosphetane. From the comparison of the reaction of Ph(3)P=CH(1-Ad) + benzaldehyde with those of Ph(3)P=CH(CH(2))(2)CH(3) + benzaldehyde and benzophenone, and Ph(3)P=CH(CH(3))(2) + benzophenone, it was concluded that all the reactions with these nonstabilized ylides proceed via an electron-transfer mechanism and that the rate-determining step changes from the electron transfer step to that of radical combination when the substrate or ylide becomes more sterically demanding.

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Electron transfer in the reaction of benzaldehyde with a nonstabilized ylide

Cited by 22 publications

References 19 publications

The modern interpretation of the Wittig reaction mechanism

The modern interpretation of the Wittig reaction mechanism

Reactions of PhSCH₂Li and NCCH₂Li with Benzaldehyde and Benzophenone: When Does the Mechanism Change from ET to Polar?

Detection and Reaction of Oxaphosphetanes Derived from Benzaldehyde and 1-Adamantylmethylidene Ylide

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Electron transfer in the reaction of benzaldehyde with a nonstabilized ylide

Cited by 22 publications

References 19 publications

The modern interpretation of the Wittig reaction mechanism

The modern interpretation of the Wittig reaction mechanism

Reactions of PhSCH2Li and NCCH2Li with Benzaldehyde and Benzophenone: When Does the Mechanism Change from ET to Polar?

Detection and Reaction of Oxaphosphetanes Derived from Benzaldehyde and 1-Adamantylmethylidene Ylide

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Reactions of PhSCH₂Li and NCCH₂Li with Benzaldehyde and Benzophenone: When Does the Mechanism Change from ET to Polar?