Angew. Chem. Int. Ed. 2022. 202206446

Indene and other arene derivatives are found in many biologically active pharmaceutical molecules and functional materials. We used a newly investigated CCC pincer Ir^III catalyst (SNIr−H)(Sci. China Chem. 2020, 63, 1761–1766). Excellent regioselectivity and yield (89 %) of the C3-alkylated indenes were obtained. Additionally, the challenging sp²C-alkylation was readily accomplished. This method could be utilized for the synthesis of the analogs of a histamine H1 receptor antagonist and the functional material template molecule, indeno[2,1-a]indene. A hemilabile Ir^III-dihydride intermediate was proposed based on control experiments for the borrowing hydrogen mechanism and is key to the success of this Ir^III catalyst in the reduction of unactivated multi-substituted olefin intermediates. In this catalytic system, a series of side reactions in which alcohols participate in the process of hydrogen borrowing and reducing hydrogen can be avoided to a large extent, such as Aldol and Tishchenko reactions.