Cp*CoIII Catalyzed Site‐Selective CH Activation of Unsymmetrical O‐Acyl Oximes: Synthesis of Multisubstituted Isoquinolines from Terminal and Internal Alkynes

The synthesis of isoquinolines by site‐selective CH activation of O‐acyl oximes with a Cp*CoIII catalyst is described. In the presence of this catalyst, the CH activation of various unsymmetrically substituted O‐acyl oximes selectively occurred at the sterically less hindered site, and reactions with terminal as well as internal alkynes afforded the corresponding products in up to 98 % yield. Whereas the reactions catalyzed by the Cp*CoIII system proceeded with high site selectivity (15:1 to 20:1), use of the corresponding Cp*RhIII catalysts led to low selectivities and/or yields when unsymmetrical O‐acyl oximes and terminal alkynes were used. Deuterium labeling studies indicate a clear difference in the site selectivity of the CH activation step under Cp*CoIII and Cp*RhIII catalysis.