Chiral N-Heterocyclic Carbene Catalyzed, Enantioselective Oxodiene Diels−Alder Reactions with Low Catalyst Loadings

• Published in: Journal of the American Chemical Society Vol. 128; no. 47; pp. 15088 - 15089
• Main Authors: He, Ming, Uc, Gerson J, Bode, Jeffrey W
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 29-11-2006
• Subjects: Aldehydes - chemistry; Alkenes - chemistry; Catalysis; Catalysts: preparations and properties; Chemistry; Exact sciences and technology; General and physical chemistry; Heterocyclic Compounds - chemistry; Hydrocarbons - chemistry; Ketones - chemistry; Lactones - chemical synthesis; Methane - analogs & derivatives; Methane - chemistry; Stereoisomerism; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Carbene; Catalytic reaction; Enantioselectivity; Nitrogen heterocycle; Organic free biradical; Diels Alder addition; Chiral compound; Catalyst
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja066380r

Chiral N-heterocyclic carbene (NHC) catalyzed redox reactions of racemic α-chloroaldehydes lead to the generation of chiral enolates suitable for highly enantioselective inverse-electron-demand 1-oxodiene Diels−Alder reactions. Significantly, these reactions proceed under mild, operationally friendly reaction conditions (EtOAc, room temperature, 2−8 h) using less than 1 mol % of a chiral N-mesityl triazolium salt as the precatalyst. A broad array of densely functionalized dihydropyran-2-ones bearing either aliphatic or aromatic substiutents are formed in excellent yields and exceptional enantioselectivities from readily available reactants. Stereochemical mismatching between the racemic starting materials and the chiral catalyst is avoided by rapid epimerization of the chloroaldehydes under the reaction conditions.