NIS-mediated iodocyclization of N-sulfonyl propargylamides for the synthesis of various oxazolidines and iodoalkylidenedihydrooxazoles via a 5-exo-dig process is developed. The resulting iodoalkylidenedihydrooxazoles can be further transformed into the corresponding oxazoles in the presence of dioxygen.
Silver(I)-catalyzed [3,3] rearrangement of N-sulfonyl propargylamides affords functionalized oxazoles with highly regioselective migration of the sulfonyl group by the introduction of acyloxy groups. The allenylamides, generated from the corresponding propargylamides, can also undergo the silver-catalyzed cyclization to give various 5-vinyloxazoles.
An unprecedented formal [3+2] annulation of propargylamides with TMSN3 to deliver functionalized tetrazoles is developed. Oxygen-atom transfer (OAT) from the amide group to the C≡C bond was realized via a NIS-triggered-cyclization/ring-opening cascade pathway. The OAT process enables the amide to serve as a two-atom unit in the reactions. Notably, in situ umpolung of azide occurred when terminal propargylamides were employed in this reaction, providing an array of diiodomethylated dihydroimidazoles.
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