Chiral Lewis Acid-Catalyzed Enantioselective Cycloadditions between Indoles and Cyclic Carbonyl Ylides Derived from Diazodiketone or Diazoketoester Derivatives.

Abstract

Asymmetric 1,3-dipolar cycloaddition reactions between N-methylindoles and several cyclic carbonyl ylides that were derived from diazodiketone or diazoketoester precursors in the presence of both achiral Rh and chiral lanthanoid metal catalysts are described. For the six-membered cyclic carbonyl ylides derived from 1-diazo-5-aryl-2,5-pentanedione precursors, the cycloaddition reactions were carried out using Rh2(OAc)4 (2 mol %) and the chiral Pybox-Ph2-Lu(OTf)3 complex (10 mol %) as catalysts, resulting in high enantioselectivities (83% to >98% ee (exo)) along with relatively good exo-selectivities (exo:endo = 65:35 to 94:6) and yields (63-85%). For the five-membered cyclic carbonyl ylide derived from 1-diazo-2,4-pentandione precursor, the cycloaddition reaction with 5-bromo-1-methylindole was carried out in the presence of Rh2(OAc)4 (2 mol %) and the chiral Pybox-Ph2-Er(OTf)3 complex (30 mol %) as catalysts, resulting in relatively good enantioselectivity (78% ee) and endo-selectivity (endo:exo = 81:19).