Catalytic Divergent [3+3]‐ and [3+2]‐Cycloaddition by Discrimination Between Diazo Compounds

Highly selective divergent cycloaddition reactions of enoldiazo compounds and α‐diazocarboximides catalyzed by copper(I) or dirhodium(II) have been developed. With tetrakis(acetonitrile)copper(I) tetrafluoroborate as the catalyst epoxypyrrolo1,2‐a]azepine derivatives were prepared in good yields and excellent diastereoselectivities through the first reported 3+3]‐cycloaddition of a carbonyl ylide. Use of Rh₂(pfb)₄ or Rh₂(esp)₂ directs the reactants to regioselective 3+2]‐cycloaddition generating cyclopenta2,3]pyrrolo2,1‐b]oxazoles with good yields and excellent diastereoselectivities.