Mechanistic Insights on Orthogonal Selectivity in Heterocycle Synthesis

Recently, we have developed a method for catalytic regioselective synthesis of 2-substituted and 3-substituted benzofurans starting from phenols. The choice of reacting partner, olefin versus alpha,beta-unsaturated acid, is critical to dictate the isomeric product formation. Instances are known where these olefinic partners did not complement each other and yield a similar outcome. In the current work, we have addressed this paradox with emphasis on (a) the origin of orthogonal selectivity and (b) the key requirements to expect complementary behavior. Experimental and computational studies provided important mechanistic insights. Electrostatic compatibility during migratory insertion and the positioning of the carboxylic acid moiety in catalytic steps are found to exert a paramount impact in determining the regioselectivity. The study offers a predictable single component tuning tool to control the regioselectivity.