title: Computational analysis of the stereochemical outcome in the imidazolidinone-catalyzed enantioselective (4 + 3)-cycloaddition reaction.
abstract: Computations show why the catalytic, asymmetric (4 + 3)-cycloaddition reaction developed in the Harmata laboratories proceeds with facial selectivity opposite to that for models proposed for related catalyzed Diels-Alder reactions. Computations with M06-2X/6-311+G(d,p)//B3LYP/6-31G(d) show that iminium ions derived from MacMillan's chiral 2-tert-butyl-5-benzylimidazolidinone and siloxypentadienals undergo (4 + 3)-cycloadditions with furans preferentially on the more crowded face. Conformational reorganization of the benzyl group, to avoid intramolecular interaction with the silyl group, is responsible for differentiating the activation barriers of top- and bottom-face attack.
authors.affiliation: School of Chemistry and Molecular Biosciences, University of Queensland , Brisbane, QLD 4072, Australia.
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Krenske
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.forename: Michael
authors.initials: M
authors.lastname: Harmata
mesh_terms: D002384:Catalysis; D039301:Computers, Molecular; D061565:Cycloaddition Reaction; D005663:Furans / Q000737:chemistry*; D006827:Hydantoins / Q000032:analysis* / Q000737:chemistry*; D008962:Models, Theoretical; D008968:Molecular Conformation; D015394:Molecular Structure; D012833:Siloxanes / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D005663:Furans; D006827:Hydantoins; D012833:Siloxanes