Rhodium-Catalyzed Synthesis of Isoquinolones

Significance

The rhodium(III)-catalyzed synthesis of isoquinolones 3 from hydroxamic acid derivatives 1 and acetylenes 2 is reported. The reaction is equally tolerant of EDGs and EWGs on the aromatic ring. For meta-substituted substrates the rhodation occurs exclusively at the least sterically hindered position leading to the C7-substituted isoquinolones. Symmetrical and unsymmetrical acetylenes both participate efficiently in the ­reaction. In the case of alkyl-aryl-disubstituted alkynes, the sp^² center is installed selectively at the 3-position (R^³). A mechanism is postulated on the basis of deuteration and competition experiments.