Regioselective annulation of propargyl alcohols with ambident-enols: A Ca(II)-catalyzed trisubstituted benzochromene synthesis

Abstract

Highly regioselective, 6-endo cyclization between propargyl alcohols and ambident enols such as naphthols, 4-hydroxy coumarin, cyclohexane-1,3-dione, 5,5-dimethylcyclohexane-1,3-dione is described using Ca(OTf)2 under solvent free conditions. The reaction proceeds through a cascade annulation which involves an etherification, Claisen type rearrangement, allene formation and endocyclization. Further, we extended this method to the synthesis of iodo-derivative and demonstrated the reactivity in cross-coupling reactions.