An isokinetic relationship in the oxidation of acetals by ozone. Evidence for rotation before the oxidation of acyclic acetals

Taillefer, Roland J.; Thomas, Shirley E.; Nadeau, Yves; Beierbeck, Helmut

doi:10.1139/v79-495

Cited by 10 publications

(4 citation statements)

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“…The kinetic method used to measure slow rates at low temperatures in ethyl acetate as solvent has been described previously (4). Rapid rates (solvent CCI,; 0-3S0C, dioxolane acetals I) were measured by stop-flow techniques using a Durrum-Gibson D-130 instrument, equipped with a reaction cuvette of 20 mm, a Jarrel-Ash 0.25 m monochromator with deuterium lamp.…”

Section: Kineticsmentioning

confidence: 99%

“…These are depicted in Scheme 3. The possibility that the hydride transfer mechanism (Scheme 3a) might be operative arises from the strong conformational effects observed in these reactions (2)(3)(4). Antiperiplanar lone pairs will elongate the C-H bond as well as stabilize the incipient dioxonium ion.…”

Section: Substituent Effectsmentioning

confidence: 99%

“…, , OR' ,OR' In 1971, it was first reported (I) that aldehyde Experimental evidence was also provided (2)(3)(4) to suggest that for oxidation to proceed, it is required that one non-bonded electron pair on each oxygen of the acetal function lies antiperiplanar to the C-H bond of the acetal function (Scheme 1). Recently, it was shown (5) that an acetal hydrotrioxide (A, Scheme 2) is an intermediate in the reaction, and that singlet oxygen is produced during its unimolecular decomposition (5).…”

Section: Introductionmentioning

confidence: 99%

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The mechanism of oxidation of acetals by ozone. I. Stoichiometry, order of the reaction, solvent effects, and substituent effects

Taillefer¹,

Thomas²,

Nadeau³

et al. 1980

Can. J. Chem.

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A systematic investigation of the reaction between ozone and acetals to form acetal hydrotrioxides A has been undertaken. The stoichiometry of the reaction has been shown to be 1:l in each reactant and the order of the reaction was also one in each reactant. Substituent effects measured in a variety of systems and under several conditions of temperature and solvent were found to be small (p = -1.10 to -1.58). Solvent polarity was also found to have little effect on the rate of the reaction. Mechanistically, these facts are interpreted in terms of a 1.3-dipolar insertion of ozone into the C-H bond of the acetal function.ROLAND J. TAILLEFER, SHIRLEY E. THOMAS, YVES NADEAU, S. FLISZAR et HERVE HENRY. Can. J. Chem. 58, 1138Chem. 58, (1980. Une etude systematique de la rtaction de I'ozone avec les acetals pour former les acktals hydrotrioxides A a t t t entreprise. On a trouve que la stoechiomttrie et I'ordre de la reaction etaient de un dans chacun des reactifs. L'effet des substituents sur la vitesse de reaction, mesure dans plusieurs systimes et sous difftrentes conditions de temperatures et de solvants est faible (p = -1.108 -1.58) de mime que I'effet de la polarit6 des solvants. Ces faits sont interpretis en invoquant un mecanisme d'addition 1,3-dipolaire de I'ozone dans le lien C-H de la fonction acetale.

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Section: Kineticsmentioning

confidence: 99%

Section: Substituent Effectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The mechanism of oxidation of acetals by ozone. I. Stoichiometry, order of the reaction, solvent effects, and substituent effects

Taillefer¹,

Thomas²,

Nadeau³

et al. 1980

Can. J. Chem.

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“…The scope and mechanism of the rapid and efficient oxidation of acetals with ozone were described in detail by Deslongchamps, Taillefer and co-workers. [33][34][35][36][37][38] 3 ppm for the gem-dimethyl groups. 41 To complete the sequence, the primary TBS ether in 33 was selectively cleaved using HF•pyridine in tetrahydrofuran at room temperature to afford pure 2 in 72% yield.…”

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confidence: 99%

A Formal Synthesis of Ionomycin Featuring a Permanganate-Mediated Oxidative Cyclisation

Li¹,

Cooksey²,

Gao³

et al. 2010

Synthesis

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Key steps in a synthesis of the C17-C32 fragment of ionomycin are (a) an auxiliary-directed oxidative cyclisation of a diene with potassium permanganate to construct a tetrahydrofuran ring and four stereogenic centres in a single operation, and (b) a chainappendage reaction featuring the alkylation of an enolsilane by an oxocarbenium ion generated from a 2-phenylsulfonyl-substituted tetrahydrofuran.Ionomycin (1) is an ionophore isolated from Streptomyces conglobatus with a high affinity for divalent cations. 1-3 A detailed competitive binding study revealed the following selectivity: Pb 2+ > Cd 2+ > Zn 2+ > Mn 2+ > Ca 2+ > Cu 2+ > Co 2+ > Ni 2+ > Sr 2+ . 4 It is widely used as a tool in cell biology for the investigation of processes requiring calcium mobilisation and its use in lead detoxification has been mooted. In 2009 we reported a total synthesis of ionomycin and its calcium complex based on (a) a highly stereoselective Au 3+ -catalysed cycloisomerisation of an ahydroxyallene to create the tetrahydrofuran B, and (b) a rhodium-catalysed rearrangement of an a-diazo-b-hydroxyketone to generate the b-diketone moiety. 5 A key intermediate in our synthesis was the C17-C32 alcohol 2 (Scheme 1), which had also featured in the preceding syntheses developed by Evans 6 and Hanessian 7 reported in 1990. 8 We now report an alternative synthesis of the C17-C32 alcohol 2, and hence a formal synthesis of ionomycin, which features (a) a permanganate-mediated oxidative cyclisation reaction 9 to create the tetrahydrofuran ring A in fragment 4 and four of its stereogenic centres in a single operation, and (b) a Ley a-heteroalkylation reaction to append fragment 3 to C23 of fragment 4.The anti,anti-stereotriad in fragment 3 was installed by a crotylmetallation reaction on the known aldehyde 8 (Scheme 2). 10 Initial attempts to use Roush's easily accessible tartrate-derived (E)-crotylboronic ester reagent 9 were thwarted by poor diastereoselectivity (dr = 2:1). [11][12][13] Better results were obtained with (E)-crotyldiisopinocampheylborane (10) derived from (+)-a-pinene; in this case the desired adduct 11 was obtained in a modest 52% yield but excellent diastereoselectivity (dr >95:5). 14 The yield and diastereoselectivity of the crotylmetallation reaction were very sensitive to the quality of the reagent 10, with the best results being obtained with freshly prepared reagent. 15 After protection of the secondary alcohol as its pmethoxybenzyl ether, the alkene function of 12 was converted into the ketone 13 through a Wacker oxidation. 16 Finally, the ketone was converted into its enolsilane derivative in the usual way, to afford fragment 3 in 30% overall yield from commercial ester 5.

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Anomeric Effect: Origin and Consequences

Graczyk

Mikołajczyk

1994

Topics in Stereochemistry

126

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An isokinetic relationship in the oxidation of acetals by ozone. Evidence for rotation before the oxidation of acyclic acetals

Cited by 10 publications

References 6 publications

The mechanism of oxidation of acetals by ozone. I. Stoichiometry, order of the reaction, solvent effects, and substituent effects

The mechanism of oxidation of acetals by ozone. I. Stoichiometry, order of the reaction, solvent effects, and substituent effects

A Formal Synthesis of Ionomycin Featuring a Permanganate-Mediated Oxidative Cyclisation

Anomeric Effect: Origin and Consequences

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