The scope of oxyamination of alkenes has been greatly expanded using various transition metals, whereas the corresponding reactions of alkynes remain underdeveloped. In this regard, we envisioned the formation of metal-acylnitrenoid from O-acyl hydroxylamine derivatives (A) followed by a carboxyamidation with an appropriately tethered alkyne. If an internal delivery of the carboxylate through a concerted mechanism (IN-A) occurs, cis-addition product B is expected. Depending on the substituent X–Y in B, the acyloxy-substituted exo-alkene would participate in π-bond migration, O→N, O→C, and O→O acyl group migrations. We found iron catalyst FeL3 is the most efficient catalyst to render carboxyamidation product B in Z-selective fashion. Isomerization of B promoted by 4-(dimethylamino)pyridine smoothly formed products C, D, and F except for O→C acyl migrated product E. In general, N-acyloxycarbamates undergo π-bond migration to form 2-(3H)oxazolones C while arene-tethered and Z-alkene-tethered O-acylhydroxamates generate isoindolinone D and pyrrole derivative F via O→N and O→O acyl migration, respectively. Crossover experiments with substrates bearing different N-acyloxy groups and alkynyl substituents did not generate carboxylates exchanged products under optimal FeL3-catalyzed conditions. This result in combination with the Z-stereochemistry of the N,O-additions supports an internal delivery of carboxylate from the putative nitrenoid to the tethered alkyne moiety.

Transition metal-catalyzed intramolecular carboxyamidation of alkynes and subsequent isomerization reactions

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