Cycloisomerization of Alkyne‐TetheredN‐Acyloxycarbamates to 2‐(3H)Oxazolones through Nitrenoid‐Mediated Carboxyamidation

Abstract

AbstractThe cycloisomerization of alkyne‐tetheredN‐benzoyloxycarbamates to 2‐(3H)oxazolones is described. Two catalytic systems are tailored for intramolecular 5‐exo‐alkyne carboxyamidation and concomitant alkene isomerization. PtCl2/CO (5 mol%, toluene, 100 °C) promotes both carboxyamidation and alkene isomerization but has a limited substrate scope. On the other hand, FeCl3(5 mol%, CH3CN, 100 °C) promotes carboxyamidation effectively but a cocatalyst is required for the exocyclic alkene isomerization. Thus, a two‐step one‐pot protocol has been developed for a broader reaction scope, which involves FeCl3‐catalyzed carboxyamidation and base‐induced alkene isomerization. Crossover experiments suggest that these reactions proceed mainly through a mechanism involving acylnitrenoid intermediates rather than carbenoid intermediates.