Pyrylium-mediated transformations of natural products. Part 1. Synthesis and hydrolysis of 4-(4-methoxy-3-sulphophenyl)-2,6-bis-(4-sulphophenyl) pyrylium perchlorate: a new water-soluble pyrylium cation

Katritzky, Alan R.; Rosa, Michael De; Grzeskowiak, Nicholas E.

doi:10.1039/p29840000841

Cited by 15 publications

(4 citation statements)

References 6 publications

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“…Further comparisons of pK R values are shown in Chart 1. Apart from the influence of benzoannellation they illustrate the stabilizing effects of an endocyclic oxygen 47 or π-bond, as well as coordination by an Fe(CO) 3 group. 20 The low stability of the fluorenyl cation 48 is also apparent and, by contrast, the stability conferred by addition of a methylene bridge 11 to the benzhydryl cation.…”

Section: Discussionmentioning

confidence: 99%

Stabilities and Partitioning of Arenonium Ions in Aqueous Media

2008

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The phenathrenonium ion is formed as a reactive intermediate in the solvolysis of 9-dichloroacetoxy-9,10-dihydrophenanthrene in aqueous acetonitrile and undergoes competing reactions with water acting as a base and nucleophile. Measurements of product ratios in the presence of azide ion as a trap and 'clock' yield rate constants kp = 3.7 x 10(10) and kH2O = 1.5 x 10(8) s(-1), respectively. Combining these with rate constants for the reverse reactions (protonation of phenanthrene and acid-catalyzed aromatization of its water adduct) gives equilibrium constants pKa = -20.9 and pK(R) = -11.6. For a series of arenonium and benzylic cations, correlation of log kp with pKa, taking account of the limit to kp set by the relaxation of water (10(11) s(-1)), leads to extrapolation of kp = 9.0 x 10(10) s(-1) and pKa = -24.5 for the benzenonium ion and kp = 6.5 x 10(10) s(-1) and pKa = -22.5 for the 1-naphthalenonium ion. Combining these pKa's with estimates of equilibrium constants pKH2O for the hydration of benzene and naphthalene, and the relationship pKR = pKa + pKH2O based on Hess's law, gives pKR = -2.3 and -8.0 respectively, and highlights the inherent stability of the benzenonium ion. A correlation exists between the partitioning ratio, kp/kH2O, for carbocations reacting in water and KH2O the equilibrium constant between the respective reaction products, i.e., log(kp/kH2O) = 0.46pKH2O - 3.7. It implies that kp exceeds kH2O only when KH2O > 10(8). This is consistent with the proton transfer (a) possessing a lower intrinsic reactivity than reaction of the carbocation with water as a nucleophile and (b) being rate-determining in the hydration of alkenes (and dehydration of alcohols) except when the double bond of the alkene is unusually stabilized, as in the case of aromatic molecules.

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Section: Discussionmentioning

confidence: 99%

Stabilities and Partitioning of Arenonium Ions in Aqueous Media

2008

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“…Katritzky pyridinium salts, [25][26][27] easily prepared in one step by the condensation of pyrylium salts with primary amines, are air and moisture-stable and convenient for purification via filtration. Recently, Katritzky salts have been widely investigated as precursors for the generation of alkyl radical species and the subsequent cross-coupling reactions.…”

Section: Introductionmentioning

confidence: 99%

From simple Katritzky salts to AIEgens: mechanochromic luminescence and heparin detection

Lin

Yang

Liu

et al. 2020

Mater. Chem. Front.

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“…We have reported the kinetics of the reactions of such pyrylium salts with water and the equilibria existing between the pyrylium salt, the corresponding unsaturated 1 $diketone, and the enolate anion of this diketone. 2 We also previously considered the reactions of such pyrylium salts with primary amines from both the kinetic3 and preparative points of view.4 Finally we have shown that the corresponding pyridinium salts can undergo nucleophilic displacement reactions in which the pyridine behaves as the leaving group.' In all these respects, the watersoluble pyrylium-pyridinium chemistry parallels that previously carried out in non-aqueous solvents.…”

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confidence: 99%

Pyrylium-mediated transformations of natural products. Part 8. Kinetics of nucleophilic displacements with pyridines as leaving groups in aqueous solution.

Katritzky¹,

Gonzalez-Gazulla²

1985

J. Chem. Soc., Perkin Trans. 2

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Good second-order kinetics were found with k, values which were ca. 50 times less for piperidine displacements in H,O than in chlorobenzene solutions, as expected from the polarity increase. Rates for thioglycolate dianion displacements were about five times faster than for piperidine. The rate dependence on pyridine leaving group structure paralleled that previously found for non-aqueous solutions except that an additional SO3substituent group showed a small rate-decreasing effect.Earlier Parts have described the preparation of water-soluble pyrylium salts containing one or more sulphonic or carboxylic

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Pyrylium-mediated transformations of natural products. Part 1. Synthesis and hydrolysis of 4-(4-methoxy-3-sulphophenyl)-2,6-bis-(4-sulphophenyl) pyrylium perchlorate: a new water-soluble pyrylium cation

Cited by 15 publications

References 6 publications

Stabilities and Partitioning of Arenonium Ions in Aqueous Media

Stabilities and Partitioning of Arenonium Ions in Aqueous Media

From simple Katritzky salts to AIEgens: mechanochromic luminescence and heparin detection

Pyrylium-mediated transformations of natural products. Part 8. Kinetics of nucleophilic displacements with pyridines as leaving groups in aqueous solution.

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