Cycloisomerization of Alkyne-Tethered N-Acyloxycarbamates to 2-(3H)Oxazolones through Nitrenoid-Mediated Carboxyamidation

The cycloisomerization of alkyne-tethered N-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 degrees C) promotes both carboxyamidation and alkene isomerization but has a limited substrate scope. On the other hand, FeCl3 (5 mol%, CH3CN, 100 degrees 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.

Automated summary

The cycloisomerization of alkyne-tethered N-benzoyloxycarbamates to 2-(3H)oxazolones is reported. Two catalytic systems are developed for intramolecular 5-exo-alkyne carboxyamidation and alkene isomerization. PtCl2/CO and FeCl3 are effective catalysts, but FeCl3 requires a cocatalyst for alkene isomerization. A two-step one-pot protocol is established for a broader reaction scope, involving FeCl3-catalyzed carboxyamidation and base-induced alkene isomerization. Crossover experiments suggest the involvement of acylnitrenoid intermediates in these reactions.