Fig. 3: Substrate scope for nucleophilic ring opening of ABB using indole and other N-heterocycles; installation of indole-azetidine in bioactive molecules, marketed drugs, and fatty acids.

[a] Reaction condition: 2 (0.2 mmol), nucleophile (0.4 mmol), pTSA.H2O (10 mol%), HFIP (0.2 mL), after removal of HFIP add Et3N (0.8 mmol), Boc2O (0.4 mmol), DCM (5 mL). [b] TFA (10 mol%) instead of pTSA.H2O. The regioisomeric ratio (r.r.) was determined from the 1H NMR integration values.