Intramolecular Schmidt reactions of alkyl azides with ketals and enol ethers

Article abstract of DOI:10.1016/0040-4020(96)00037-3

The ketals or enol ethers of 1,5-azidoketones were converted into lactams using a two-stage process. Treatment of the ketals and enol ethers with acid (trifluoroacetic acid, triflic acid, or trimethylsilyl triflate) afforded an oxonium ion which reacted with the tethered azide to give a 1,1-azido-alkoxy intermediate. Bond reorganization led to an iminium ether that was reacted with sodium iodide in acetone to expose the amide products. Seven intramolecular examples proceeding in yields of 68 to ≥95% are reported using dimethyl or diethyl ketals. Attempts using 1,3-dioxolanes and an intermolecular example are also described.