172923-77-2 New strategy for the total synthesis of macrosphelides A and B based on ring-closing metathesis

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(Matrix presented) A new total synthesis of macrosphelides A and B using ring-closing metathesis (RCM) as a macrocyclization step is described. The substrate of the RCM could be synthesized from readily available chiral materials, methyl (S)-(+)-3-hydroxybutyrate and methyl (S)-(-)-lactate, with a high efficiency. The RCM proceeded in the presence of Grubbs' Ru-complex, providing a new effective synthetic route to these natural products. https://www.lookchem.com/CASDataBase_172923-77-2.htm

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75-75-2 Solvolyses of Secondary Sulfonates in Aqueous Ethanol and Acetone. Nonlinear mY Relationships due to Leaving Group and Medium Effects

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Solvolitic rate constants for secondary mesylates and tosylates in aqueous ethanol and in aqueous acetone are correlated with Winstein-Grunwald Y values.Curvature of these plots is greatest for tosylates in aqueous ethanol, especially for 2-adamantyl.Because mesylates show little or no curvature, it is argued that the results cannot be explained by mechanistic changes but by solvation effects of the leaving group in the mixed solvents.The parameter, m, measuring response to solvent ionizing power varies from 0.68 for isopropyl to 1.21 for 2-adamantyl mesylate in aqueosus acetone at 25 deg C.An alternative solvent ionizing power parameter for tosylates, Y OTs , and the solvent nucleohpilicity parameter, N OTs , are evaluated for 20percent ethanol/water, 20percent acetone/water, and 40percent acetone/water.It is proposed that solvolyses of substrates having the same (or very similar) leaving group should be compared if reliable mechanistic information (e.g., nucleophilic solvation effec...
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100-64-1 On the Oxidation of Hydroxylamines with o -Iodoxybenzoic Acid (IBX)

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o -Iodoxybenzoic acid (IBX) is confirmed as a powerful tool for the oxidation of hydroxylamines. The synthetic route is demonstrated as efficient and user friendly, and is exploited on various carbohydrate-derived N,N-disubstituted hydroxylamines (cyclic, acyclic, and functionalized ones), affording the corresponding nitrones in good yields and regioselectivity. N-Monosubstituted hydroxylamines revealed an interesting divergent behavior depending on the reaction conditions. While IBX oxidation in dimethyl sulfoxide at 45 °C furnished oximes as reported, the oxidation in dichloromethane at room temperature afforded efficiently the unusual corresponding nitroso dimers. https://www.lookchem.com/CASDataBase_100-64-1.htm
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100-15-2 Alkyl Nitrite-Metal Halide Deamination Reactions. 7. Synthetic Coupling of Electrophilic Bromination with Substitutive Deamination for Selective Synthesis of Multiply Brominated Aromatic Compounds from Arylamines

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Aromatic amines undergo substitution with copper(II)bromide that is in competition with substitutive deamination when these reactions are performed with tert-butyl nitrite.Except for the exceptionally reactive 4-substituted 1-aminonaphthalenes,which undergo selective bromine substitution at the 1- and 2-positions in relatively high isolated yields,rates for oxidative bromination and substitutive deamination are not sufficiently different that selective multiple bromination can be achieved.Oxidative bromination of N,N-dimethylaniline by copper(II)bromide occurs with partial dealkylation,and nitration products are observed from reactions performed with copper(II)bromide and tert-butyl nitrite.Implications of these results for the successful utilization of copper(II)bromide/tert-butyl nitrite combinations in substitutive deamination reactions of aromatic amines are discussed.Multiply brominated aromatic compounds are produced from aromatic amines in high yield through treatment of the aro...
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