Carbon-Phosphorus Heterocycles. A Study of the Mechanism of Cyclization of Alkenyl-Substituted Phosphium Salts by 115% Polyphosphoric Acid via Stereochemical and Phosphorus-31 Nuclear Magnetic Resonance Analyses

Purdum, W. R.; Dilbeck, G. A.; Berlin, K. Darrell

doi:10.1021/jo00913a616

Cited by 8 publications

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“…The latter observation was rationalized on the basis of a rapidly formed intermediate of a classic type in electrophilic substitution. 282 Recently, the above procedure has been extended to include C-P heterocyclic systems with a carbonyl group in the molecule. 225 For example, phosphonium salts represented by 276 cyclized smoothly with 115% PPA to afford benzophospheninium salts 277 in modest yields (40-50%).…”

Section: F Electrophilic Additions and Cyclizationsmentioning

confidence: 99%

Polycyclic carbon-phosphorus heterocycles

et al. 1977

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Section: F Electrophilic Additions and Cyclizationsmentioning

confidence: 99%

Polycyclic carbon-phosphorus heterocycles

et al. 1977

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“…[10] To avoid undesired rearrangement, Berlin used polyphosphoric acid (115 %) at elevated temperatures to perform the intramolecular Friedel-Crafts reaction of allyltriphenyl phosphonium salts. [11] In situ formation of ad ication was postulated in this seminal contribution, whose hypothesis was recently reformulated by Va silyev and Stankevič (Scheme 1a). [12] Laali et al [13] and Klumpp et al [14] went astep further by,respectively,showing the protonation of tetraphosphocubane and ketophosphonium salts in superacids.…”

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confidence: 98%

Evidence of Phosphonium‐Carbenium Dication Formation in a Superacid: Precursor to Fluorinated Phosphine Oxides

et al. 2018

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Unambiguously confirmed by low-temperature in situ NMR experiments,X -rayd iffraction and vibrational spectroscopy, phosphonium-carbenium superelectrophiles are shown to be generated in strong acidic conditions.R epresenting crucial intermediates,t heir exploitation allows for the synthesis of unprecedented fluorinated (cyclic) phosphine oxides.Fluorinated compounds [1] are undeniably associated with the development of catalysis, [2] agrochemicals and drugs. [3] Organophosphorus compounds have found wide application in various fields such as catalysis,medicinal chemistry,material science and inorganic chemistry. [4] To our knowledge,t he formation of fluorinated phosphines and their derivatives via direct addition is limited to af ew reactions:t he trifluoromethylfluorosulfonylation, [5] theb romodifluoromethylation [6] of allyldiphenyl phosphine oxide,the nucleophile mediated reaction of Ruppert-Prakash reagent (or perfluoroalkyltrimethylsilanes) with phosphites,o ra ddition of LiC 2 F 5 to chlorinated phosphine [7] and the unimolecular radical nucleophilic substitution reaction. [8] Although the addition of an element-hydrogen pair to an unsaturated CÀCb ond is as tandard direct strategy to functionalize am olecular skeleton, hydro-(hetero)element addition to allylic or propargylic phos-phorus containing derivatives is rather limited. [9] Thep H dependent stability and the prototropic isomerization of the corresponding phosphonium derivatives may be the reason for the difficulty to selectively add any species to these derivatives under acidic conditions. [10] To avoid undesired rearrangement, Berlin used polyphosphoric acid (115 %) at elevated temperatures to perform the intramolecular Friedel-Crafts reaction of allyltriphenyl phosphonium salts. [11] In situ formation of ad ication was postulated in this seminal contribution, whose hypothesis was recently reformulated by Va silyev and Stankevič (Scheme 1a). [12] Laali et al. [13] and Klumpp et al. [14] went astep further by,respectively,showing the protonation of tetraphosphocubane and ketophosphonium salts in superacids. [15] On this basis,w ep ostulated that the generation of as uperelectrophile from an unsaturated organophosphorus compound can be expected under superacidic conditions and further exploited to produce valuable and innovative (P,F)-derivatives.W er eport here the first example of ahydrofluorination [16] and cyclization/fluorination of unsaturated phosphine oxides.T he involvement of phosphonium-carbenium superelectrophiles (Scheme 1b)i se videnced by X-ray crystallography,l ow-temperature NMR spectroscopy and DFT calculations.This work aims to address two important challenges: 1) Thed eactivation of the unsaturation after protonation of the P-containing function, which could prevent substrates from any reaction, needs to be outweighed by the high acidity Scheme1. a) Postulated and reported phosphorus containing polycations formation in acidic conditions(literature);b)Exploitation of phosphonium-carbeniumsuperelectrophiles for the synthesis of...

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