Cp?CoIII Catalyzed Site-Selective C-H Activation of Unsymmetrical O-Acyl Oximes: Synthesis of Multisubstituted Isoquinolines from Terminal and Internal Alkynes

Article abstract of DOI:10.1002/anie.201507744

The synthesis of isoquinolines by site-selective C-H activation of O-acyl oximes with a Cp?Co^III 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?Co^III system proceeded with high site selectivity (15:1 to 20:1), use of the corresponding Cp?Rh^III 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?Co^III and Cp?Rh^III catalysis. Isoquinolines are obtained by the C-H activation of O-acyl oximes with a Cp?Co^III catalyst. Whereas the reactions catalyzed by the Cp?Co^III system proceed with high site selectivity favoring C-H activation at the sterically less hindered site, the use of the corresponding Cp?Rh^III catalyst leads to low selectivities and/or yields when unsymmetrical O-acyl oximes and terminal alkynes are used.