Selective Monoalkylation\nor Dialkylation of Indenes\nwith Alcohols by Bis‑<i>N</i>‑Heterocyclic\nCarbene Manganese

Selective direct alkylation of indenes is important for\nthe synthesis\nand decoration of indene derivatives. In contrast to traditional alkylation\nmethods, using unactivated alcohol as alkylation reagents via borrowing\nhydrogen or hydrogen autotransfer is highly attractive. However, the\nnature of the high-lying lowest unoccupied molecular orbital of the\ncondensation intermediate raises a big challenge for the development\nof the BH system for the alkylation of indenes using alcohols. Through\ntuning the stability and the reactivity of the metal-hydride species\nby theoretical prediction, herein, we succeeded in developing a non-noble\nMn-catalyzed selective direct monoalkylation or dialkylation of indenes\nunder mild conditions, producing the corresponding versatile alkylated\nindenes in satisfactory yields. A broad scope of substrates including\nprimary benzylic, aliphatic, amino, hydroxyl, and second alcohols\nas well as various indenes are tolerated in the system. Additionally,\nthis method could be used for the synthesis of potential precatalyst\ncomplexes and bioactive molecules. Mechanistic studies including control\nexperiments, kinetic investigations, kinetic isotope effect, deuterium\nlabeling experiments, and density functional theory calculations,\nreveal the proper metal-hydride for a successful BH process.