Alkylation of phosphorus keto-ylids and rearrangement of o-alkylated phosphonium salts

Neomeyanov, N. A.; Berman, S. T.; Reutov, O. A.

doi:10.1007/bf01152895

Cited by 4 publications

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“…The alkylations of 2 and 13 with MeI and PhCH 2 I (Scheme a) were found to occur on oxygen at room temperature, while C-alkylated products were obtained at elevated temperature. This behavior can be rationalized by reversibility of O-alkylation at higher temperature . The isolated O-methylated adduct 21 (R 1 = R 2 = Me) was shown independently to revert to the starting keto-ylide 2 (by S N 2 attack of iodide on the OMe group), which subsequently formed 22 (R 1 = R 2 = Me) upon heating in toluene in a sealed vessel (Scheme a).…”

Section: Alkylations and Acylations Of Acceptor-substituted Phosphoni...mentioning

confidence: 96%

“…The isolated O-methylated adduct 21 (R 1 = R 2 = Me) was shown independently to revert to the starting keto-ylide 2 (by S N 2 attack of iodide on the OMe group), which subsequently formed 22 (R 1 = R 2 = Me) upon heating in toluene in a sealed vessel (Scheme a). O-Alkylations of 2 and 13 with EtI or n -PrI under the same conditions were found to be irreversible even at high temperature (Scheme a) …”

Section: Alkylations and Acylations Of Acceptor-substituted Phosphoni...mentioning

confidence: 97%

“…Reactions of carbonyl-stabilized ylides (including 1 , 2 , and 13 ) with alkyl halides (Scheme a), − ,, and [Et 3 O]BF 4 (Scheme b), have been reported to result in irreversible attachment of the alkyl group to the ylide oxygen. The reaction of ylide 19 with CH 2 Br 2 or CH 2 I 2 yielded the bis-O-alkylated phosphonium salts 20 (Scheme c) .…”

Section: Alkylations and Acylations Of Acceptor-substituted Phosphoni...mentioning

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: Alkylations and Acylations Of Acceptor-substituted Phosphoni...mentioning

confidence: 96%

Section: Alkylations and Acylations Of Acceptor-substituted Phosphoni...mentioning

confidence: 97%