Rh(III)-Catalyzed Decarboxylative Coupling of Acrylic Acids with Unsaturated Oxime Esters: Carboxylic Acids Serve as Traceless Activators

α,β-Unsaturated carboxylic
acids undergo Rh­(III)-catalyzed decarboxylative coupling with α,β-unsaturated O-pivaloyl oximes to provide substituted pyridines in good
yield. The carboxylic acid, which is removed by decarboxylation, serves
as a traceless activating group, giving 5-substituted pyridines with
very high levels of regioselectivity. Mechanistic studies rule out
a picolinic acid intermediate, and an isolable rhodium complex sheds
further light on the reaction mechanism.