Switchable polarity recyclable solvent mixtures were applied as reaction medium and catalyst to replace the conventional base catalysts in the Claisen–Schmidt condensation of 17‐oxo steroids with aromatic aldehydes. Reversibility between ionic and nonionic forms of the new 2‐n‐butyl‐1,1,3,3‐tetramethylguanidine (nBu‐TMG)/ethylene glycol/CO2 and 2‐tert‐butyl‐1,1,3,3‐tetramethylguanidine (tBu‐TMG)/ethylene glycol/CO2 systems were proved by conductivity measurements. The structure of the ionic form was established by 1H NMR and IR measurements and by quantum chemical calculations. The steroidal products with androstane and estrane skeleton were characterised with spectroscopic methods (NMR, IR, MS).