Diastereoselective 1,3-Dipolar Cycloaddition of Nitrones to Donor–Acceptor Cyclopropanes Catalyzed by a Calcium(II) Complex

Calcium triflate has been identified as an efficient catalyst for the cycloaddition of nitrones to donor–acceptor cyclopropanes. The reaction proceeds with good to excellent yields of the corresponding tetrahydro-1,2-oxazines with high levels of diastereoselectivity. The generality of the reaction allowed for the synthesis of tetrahydro-1,2-oxazines bearing alkyl, aryl, and heteroaromatic substitution.