RESUMEN
While the modular construction of molecules from suitable building blocks is a powerful means to more rapidly generate a diversity of molecules than through customized syntheses, the further evolution of the underlying coupling methodology is key to realize widespread applications. We herein disclose a complementary modular coupling approach to the widely employed Suzuki coupling strategy of boron containing precursors, which relies on organogermane containing building blocks as key orthogonal functionality and an electrophilic (rather than nucleophilic) unmasking event paired with air-stable PdI dimer based bond construction. This allows to significantly shorten the reaction times for the iterative coupling steps and/or to close gaps in the accessible compound space, enabling straightforward access also to iodinated compounds.
RESUMEN
In this work, the reactivities of acetonyl and benzoyl radicals in aromatic substitution and addition reactions have been compared in an experimental and computational study. The results show that acetonyl is more electrophilic than benzoyl, which is rather nucleophilic. A Hammett plot analysis of the addition reactions of the two radicals to substituted styrenes clearly support the nucleophilicity of benzoyl, but in the case of acetonyl, no satisfactory linear correlation with a single substituent-related parameter was found. Computational calculations helped to rationalize this effect, and a good linear correlation was found with a combination of polar parameters (σ+ ) and the radical stabilization energies of the formed intermediates. Based on the calculated philicity indices for benzoyl and acetonyl, a quantitative comparison of these two radicals with many other reported radicals is possible, which may help to predict the reactivities of other aromatic radical substitution reactions.
RESUMEN
Direct C-H functionalization can quickly increase useful structural and functional molecular complexity1-3. Site selectivity can sometimes be achieved through appropriate directing groups or substitution patterns1-4-in the absence of such functionality, most aromatic C-H functionalization reactions provide more than one product isomer for most substrates1,4,5. Development of a C-H functionalization reaction that proceeds with high positional selectivity and installs a functional group that can serve as a synthetic linchpin for further functionalization would provide access to a large variety of well-defined arene derivatives. Here we report a highly selective aromatic C-H functionalization reaction that does not require a particular directing group or substitution pattern to achieve selectivity, and provides functionalized arenes that can participate in various transformations. We introduce a persistent sulfur-based radical to functionalize complex arenes with high selectivity and obtain thianthrenium salts that are ready to engage in different transformations, via both transition-metal and photoredox catalysis. This transformation differs fundamentally from all previous aromatic C-H functionalization reactions in that it provides direct access to a large number of derivatives of complex small molecules, quickly generating functional diversity with selectivity that is not achievable by other methods.
