A Phosphine-Free Manganese Catalyst Enables Stereoselective Synthesis of (1 + <i>n</i>)‑Membered Cycloalkanes from Methyl Ketones and 1,<i>n</i>‑Diols

Herein, we report the stereoselective synthesis of (1 + n)-membered cycloalkane from methyl ketone and 1,n-diol. A manganese­(I) complex bearing a phosphine-free ligand catalyzed the reaction, which involved the formation of two C–C bonds via a sequence of intermolecular- and intramolecular-borrowing hydrogenation reactions. It produces 2 mol of water as the sole byproduct, making the process atom economical and environmentally benign. Multisubstituted cycloalkanes were obtained in good to excellent yields with very high selectivities. A thorough mechanistic analysis by high-level DFT computation rationalizes the choice of the pincer and establishes the role of hemilability of the ligand for this efficient transformation.