We report the diastereoselective cyclization of anilines with cyclobutanones and congeners by chromium catalysis. This reaction can link two strained four-membered rings with tetrahydroquinolines by forming four bonds in a diastereocontrolled manner, forming medicinally interesting cyclobutane-fused and constrained spirotetrahydroquinolines (STHQs) and complex multiple spiro carbon-containing polyazacycles. The constrained STHQs have been used as versatile feedstocks to derive a range of oxygen-, nitrogen-, and thio-substituted spiro analogues, and dioxygen-incorporated spiroazacycles.