Browsing by Subject "Arylation"

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    Room-temperature direct β-arylation of thiophenes and benzo[b]thiophenes and kinetic evidence for a Heck-type pathway
    (American Chemical Society, 2016-01-20) Colletto, Chiara; Islam, Saidul; Juliá Hernández, Francisco; Larrosa, Igor; Química Inorgánica
    The first example of a regioselective β-arylation of benzo[b]thiophenes and thiophenes at room temperature with aryl iodides as coupling partners is reported. This methodology stands out for its operational simplicity: no prefunctionalization of either starting material is required, the reaction is insensitive to air and moisture, and it proceeds at room temperature. The mild conditions afford wide functional group tolerance, often with complete regioselectivity and high yields, resulting in a highly efficient catalytic system. Initial mechanistic studies, including 13C and 2 H KIEs, suggest that this process occurs via a concerted carbo-palladation across the thiophene double bond, followed by a base-assisted anti-elimination.
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    Ru-catalyzed C–H arylation of fluoroarenes with aryl halides
    (American Chemical Society, 2016-03-04) Simonetti, Marco; Perry, Gregory J. P.; Cambeiro, Xacobe C.; Juliá Hernández, Francisco; Arokianathar, Jude N.; Larrosa, Igor; Química Inorgánica
    Although the ruthenium-catalyzed C−H arylation of arenes bearing directing groups with haloarenes is wellknown, this process has never been achieved in the absence of directing groups. We report the first example of such a process and show that unexpectedly the reaction only takes place in the presence of catalytic amounts of a benzoic acid. Furthermore, contrary to other transition metals, the arylation site selectivity is governed by both electronic and steric factors. Stoichiometric and NMR mechanistic studies support a catalytic cycle that involves a well-defined η6-arene-ligandfree Ru(II) catalyst. Indeed, upon initial pivalate-assisted C−H activation, the aryl-Ru(II) intermediate generated is able to react with an aryl bromide coupling partner only in the presence of a benzoate additive. In contrast, directing-group-containing substrates (such as 2-phenylpyridine) do not require a benzoate additive. Deuterium labeling and kinetic isotope effect experiments indicate that C−H activation is both reversible and kinetically significant. Computational studies support a concerted metalation−deprotonation (CMD)-type ruthenation mode and shed light on the unusual arylation regioselectivity.