Synthesis of 2-quinolones via palladium-catalyzed carbonylative annulation of internal alkynes by N-substituted o-iodoanilines

The palladium-catalyzed annulation of internal alkynes by N-substituted o-iodoanilines under 1 atm of carbon monoxide results in the formation of 3,4-disubstituted 2-quinolones. The nature of the substituent on the nitrogen is crucial to obtaining high yields of 2-quinolones. The best results are obtained using alkoxycarbonyl, p-tolylsulfonyl, and trifluoroacetyl substituents. The nitrogen substituent is lost during the course of the reaction resulting in the formation of N-unsubstituted 2-quinolones. A variety of internal alkynes, bearing alkyl, aryl, heteroaryl, hydroxyl, and alkoxyl substituents, are effective in this process. Electron-rich and electron-poor N-substituted o-iodoanilines, as well as heterocyclic analogues, can be employed as annulating agents.