Nitrones as Trapping Reagents of α,β‐Unsaturated Carbene Intermediates – [1,2]Oxazino[5,4‐b]indoles by a Platinum‐ Catalyzed Intermolecular [3+3] Cycloaddition

Some readily available Boc‐protected 2‐(3‐methoxy‐1‐propynyl)anilines and nitrones in platinum‐catalyzed reactions deliver 1,2]oxazino5,4‐b]indoles. Twelve examples with yields of 41–95% are reported. Different substituents like nitro, trifluoromethyl, fluoro, bromo, and ester groups are tolerated. With regard to the mechanism, this reaction probably combines an initial intramolecular cyclization/elimination to vinylcarbenoid species and a subsequent stepwise intermolecular 3+3] cycloaddition with the nitrones.