Sc(OTf)3‐catalyzed tandem (3+3)‐annulation/lactonization of cyclopropanes with salicylaldehyde nitrones to access polycyclic 1,2‐oxazines

Abstract A Sc(OTf) 3 ‐catalyzed tandem (3 + 3)‐annulation/lactonization of donor‐acceptor cyclopropane 1,1‐dieters with salicylaldehyde nitrones has been reported, affording a wide range of tetrahydrochromeno[4,3‐ c ][1,2]oxazin‐5(1 H )‐ones in moderate yields with excellent diastereoselectivities. Besides, the gram‐scale reaction has also been explored to demonstrate the utility of this protocol. Moreover, the mechanism was investigated through control experiments, which show the reaction proceeds via a tandem (3 + 3)‐annulation/lactonization reaction.