A spectral study of tautomerism in β-oxophosphonium salts

Nesmeyanov, Nic.A.; Berman, S. T.; Petrovsky, P. V.; Lutsenko, A. I.; Reutov, O. A.

doi:10.1016/s0022-328x(00)93225-x

Cited by 9 publications

(7 citation statements)

References 16 publications

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“…The benzhydrylium ion 3i obviously attacks 1 at the α-carbon to give 8i , which tautomerizes to the hydroxyvinyl phosphonium ion 9i (see Scheme ). This result is consistent with previous observations of tautomerization of β-phosphoryl , and β-phosphonium substituted aldehydes to their enol forms. When the ylide 1 is employed in excess over 3 , as in our kinetic experiments ( vide infra ), partial deprotonation of 9i by 1 is highly likely.…”

Section: Product Characterizationsupporting

confidence: 93%

“…The ultimate product, 6j , was isolated by extraction of the crude product with ethyl acetate and crystallized from ethyl acetate/cyclohexane . The residue from the extraction contained mainly 2-H (the parent phosphonium chloride salt of ylide 2 ) as a mixture of keto and enol tautomers. − …”

Section: Product Characterizationmentioning

confidence: 99%

“…Plots of lg k vs E for C-attack and O-attack (Figure ) in the reactions of 1 with 3a – f showed excellent linear correlations, from which values of N = 9.09 and s N = 0.74 (C-attack) and N = 11.86 and s N = 0.81 (O-attack) were calculated using eq for the respective nucleophilic sites of 1 (see Table ). It is not possible at present to differentiate the reactivities of the two ylide conformers ( vide supra ). ,, Since the experimental decay curves are generally monoexponential, we report a single set of values of the nucleophilicity parameters in Table .…”

Section: Reaction Ratesmentioning

confidence: 99%

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Ambident Reactivity of Acetyl- and Formyl-Stabilized Phosphonium Ylides

2016

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The kinetics and mechanism of the reactions of formyl-stabilized ylide Ph3P═CHCHO (1) and acetyl-stabilized ylide Ph3P═CHCOMe (2) with benzhydrylium ions (Ar2CH(+), 3) were investigated by UV-vis and NMR spectroscopy. As ambident nucleophiles, ylides 1 and 2 can react at oxygen as well as at the α-carbon. For some reactions, it was possible to determine the second-order rate constant for O-attack as well as for C-attack and to derive the nucleophile-specific parameters N and sN according to the correlation lg k (20 °C) = sN(E + N) for both nucleophilic sites. Generally, O-attack of benzhydrylium ions is faster than C-attack. However, the initially formed benzhydryloxyvinylphosphonium ions can only be observed by NMR spectroscopy when benzhydryl cations with high Lewis acidity are employed. In other cases, rearrangement to the thermodynamically more stable products arising from C-attack occurs. The results derived from our investigations are employed to rationalize the behavior of ambident nucleophiles 1 and 2 in reactions with carbon-centered electrophiles in general. It is shown that the principle of hard and soft acids and bases (HSAB) and the related Klopman-Salem concept of charge and orbital control lead to incorrect predictions of regioselectivity. We also show that the rate of the Wittig reaction of ylide 2 with aldehyde 14 is significantly faster than the rate of either C- or O-attack calculated using lg k (20 °C) = sN(E + N), thus indicating that the oxaphosphetane is formed by a concerted [2 + 2] cycloaddition.

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Section: Product Characterizationsupporting

confidence: 93%

Section: Product Characterizationmentioning

confidence: 99%

Section: Reaction Ratesmentioning

confidence: 99%

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Ambident Reactivity of Acetyl- and Formyl-Stabilized Phosphonium Ylides

2016

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“…The NMR spectra of 6 are indicative of a keto-enol tautomerism (Scheme 4). 40 The origin of enol formation may be hydrogen bonding to the chloride anion in non-coordinating solvents (see below). The keto-enol ratio from 1 H NMR of 56 : 44 matches the literature data of "close to 50 : 50".…”

Section: Resultsmentioning

confidence: 99%

“…The keto-enol ratio from 1 H NMR of 56 : 44 matches the literature data of "close to 50 : 50". 40 In the enol form the Ph 3 P group and the oxygen atom are cis to each other, because of the repulsion between Ph 3 P and the methyl group. ϩ Cl Ϫ with B(C 6 F 5 ) 3 where the same signal pattern could be observed.…”

Section: Resultsmentioning

confidence: 99%