The methyl groups in TetMe-IBX lower the activation energy corresponding to the rate-determining hypervalent twisting (theoretical calculations), and the steric relay between successive methyl groups twists the structure, which manifests in significant solubility in common organic solvents. Consequently, oxidations of alcohols and sulfides occur at room temperature in common organic solvents. In situ generation of the reactive TetMe-IBX from its precursor iodo-acid, i.e., 3,4,5,6-tetramethyl-2-iodobenzoic acid, in the presence of oxone as a co-oxidant facilitates the oxidation of diverse alcohols at room temperature.
Enolonium species/iodo(III)enolates of carbonyl compounds have been suggested to be intermediates in a wide variety of hypervalent iodine induced chemical transformations of ketones, including α-C-O, α-C-N, α-C-C, and α-carbon-halide bond formation, but they have never been characterized. We report that these elusive umpoled enolates may be made as discrete species that are stable for several minutes at -78 °C, and report the first spectroscopic identification of such species. It is shown that enolonium species are direct intermediates in C-O, C-N, C-Cl, and C-C bond forming reactions. Our results open up chemical space for designing a variety of new transformations. We showcase the ability of enolonium species to react with prenyl, crotyl, cinnamyl, and allyl silanes with absolute regioselectivity in up to 92 % yield.
Improved
understanding of charge-transport in single molecules
is essential for harnessing the potential of molecules, e.g., as circuit
components at the ultimate size limit. However, interpretation and
analysis of the large, stochastic data sets produced by most quantum
transport experiments remain an ongoing challenge to discovering much-needed
structure–property relationships. Here, we introduce segment clustering, a novel unsupervised hypothesis generation
tool for investigating single molecule break junction distance–conductance
traces. In contrast to previous machine learning approaches for single
molecule data, segment clustering identifies groupings of similar pieces of traces instead of entire traces. This offers a new and advantageous perspective into data set structure
because it facilitates the identification of meaningful local trace
behaviors that may otherwise be obscured by random fluctuations over
longer distance scales. We illustrate the power and broad applicability
of this approach with two case studies that address common challenges
encountered in single molecule studies: First, segment clustering
is used to extract primary molecular features from a varying background
to increase the precision and robustness of conductance measurements,
enabling small changes in
conductance in response to molecular design to be identified with
confidence. Second, segment clustering is applied to a known data
mixture to qualitatively separate distinct molecular features in a
rigorous and unbiased manner. These examples demonstrate two powerful
ways in which segment clustering can aid in the development of structure–property
relationships in molecular quantum transport, an outstanding challenge
in the field of molecular electronics.
Oxidative cleavage of a variety of olefins to the corresponding ketones/carboxylic acids is shown to occur in a facile manner with 3,4,5,6-tetramethyl-2-iodobenzoic acid (TetMe-IA)/oxone. The simple methodology involves mere stirring of the olefin and catalytic amount (10 mol %) of TetMe-IA and oxone in acetonitrile-water mixture (1:1, v/v) at rt. The reaction mechanism involves initial dihydroxylation of the olefin with oxone, oxidative cleavage by the in situ-generated 3,4,5,6-tetramethyl-2-iodoxybenzoic acid (TetMe-IBX), and oxidation of the aldehyde functionality to the corresponding acid with oxone. Differences in the reactivities of electron-rich and electron-poor double bonds have been exploited to demonstrate chemoselective oxidative cleavage in substrates containing two double bonds.
Enolonium species, resulting from the umpolung of ketone enolates by Koser's hypervalent iodine reagents activated by boron trifluoride, react with a variety of nitrogen heterocycles to form α-aminated ketones. The reactions are mild and complete in 4-5 h. Additionally, α-azidation of the enolonium species takes place using trimethylsilyl azide as a convenient source of azide nucleophile.
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