<p>This study reports a versatile and efficient strategy for the selective formation of carbon–carbon single bonds from primary and secondary alcohols via a tandem dehydrogenation–condensation–hydrogenation sequence. The transformation was evaluated using a range of solvents (toluene, DCE, dioxane, THF and MeCN) and bases (KOH, ^<i>t</i>BuOK, triethylamine, K₂CO₃ and Na₂CO₃). Conducted under continuous-flow conditions, the process delivers high selectivity within remarkably short residence times. Mechanistic elucidation supported by spectroscopic analysis, <i>in situ</i> monitoring and control experiments confirms the operation of a sequential dehydrogenation–condensation–hydrogenation pathway. A key mechanistic feature is the interconvertible coordination behavior (imino-N → Ru and amido-N–Ru) of the imidazole ligand bound to Ru(II)–para-cymene, which governs catalytic activity and selectivity. The catalyst demonstrates excellent efficiency, selectivity and functional-group tolerance. The methodology is validated through six representative examples under continuous-flow conditions, highlighting its broad applicability. Notable synthetic applications include mono-methylation and hydrogenation of unsaturated chalcones, as well as double methylation of ketones. </p> Graphical abstract <p>A continuous-fl ow Ru(II)–para-cymene catalytic process provides selective carbon–carbon single-bond formation in primary and secondary alcohols through tandem dehydrogenation–condensation–hydrogenation.</p>