Synthesis of Tetrahydro-1,2-oxazines and Pyrrolidines via Cycloadditions of Donor-Acceptor Cyclobutanes and Nitrosoarenes

During efforts to expand the scope of Lewis‐acid‐catalyzed [4+2] cycloaddition between donor–acceptor cyclobutanes and nitrosoarenes, an unexpected formation of pyrrolidine products was discovered when 50 mol‐% of MgI2 was used as a Lewis acid. It was also observed that the electronics of the nitrosoarene and judicious selection of the Lewis acid catalyst have a profound effect on the regioselectivity of the reaction. The scope of Yb(OTf)3‐catalyzed [4+2] cycloaddition between donor–acceptor (DA) cyclobutanes and nitrosoarenes is extended to additional DA cyclobutanes. Also, an unexpected formation of pyrrolidine products was discovered when 50 mol‐% of MgI2 was used as a Lewis acid with electron‐rich nitrosoarenes.