Funny you should mention that. We hoped to recover the unreacted aldehyde from the first reaction. After acidifying, we removed the solvent from the first reaction, the one performed with potassium (not cesium) carbonate. I noticed that I could still smell acetic acid or possibly the anhydride, even being at 40 °C bath temperature with a moderate vacuum. I can go a bit higher in vacuum and in temperature.
I have not yet had the chance to try a different TLC solvent, but possibly tomorrow.