Synthesis of 2,3‐dihydro‐5H‐oxazolo[2,3‐B]quinazolin‐5‐ones

Iodide‐catalyzed ring expansion of 2‐[(1‐aziridinylcarbonyl)amino]benzoic acid methyl ester (2) gave 2,3‐dihydro‐5H‐oxazolo[2,3‐b]quinazolin‐5‐one (3) in quantitative yield. Treatment of the dimethyl analog of 2 (9) with sodium iodide in acetone gave a mixture of the 2,3‐dihydro‐2,2‐dimethyl‐ (10) and 2,3‐dihydro‐3,3‐dimethyl‐5H‐oxazolo[2,3‐b]quinazolin‐5‐ones (11). However, rearrangement of 9 with sulfuric acid produced only 10. Synthesis of 11 by another route for comparison is described, and the known syntheses of 2,3‐dihydro‐5H‐oxazolo[2,3‐b]quinazolin‐5‐ones are reviewed.