title: Concerted Ring Opening and Cycloaddition of Chiral Epoxy Enolsilanes with Dienes.
abstract: Silyl-triflate-catalyzed (4+3) cycloadditions of epoxy enolsilanes with dienes provide a mild and chemoselective synthetic route to seven-membered carbocycles. Epoxy enolsilanes containing a terminal enolsilane and a single stereocenter undergo cycloaddition with almost complete conservation of enantiomeric purity, a finding that argues against the involvement of oxyallyl cation intermediates which have been previously proposed for these types of reactions. Reported are theoretical and experimental investigations of the cycloaddition mechanism. The major enantiomers of the cycloadducts are derived from S(N)2-like reactions of the silylated epoxide with the diene, in which stereospecific ring opening and formation of the two new C-C bonds occur in a single step. Calculations predict, and experiments confirm, that the observed small losses of enantiomeric purity are traced to a triflate-mediated double S(N)2 cycloaddition pathway.
authors.affiliation: School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072 (Australia). e.krenske@uq.edu.au.
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Krenske
authors.affiliation: Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P. R. China).
authors.forename: Sarah
authors.initials: S
authors.lastname: Lam
authors.affiliation: Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P. R. China).
authors.forename: Jerome P L
authors.initials: JP
authors.lastname: Ng
authors.affiliation: Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P. R. China).
authors.forename: Brian
authors.initials: B
authors.lastname: Lo
authors.affiliation: Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P. R. China).
authors.forename: Sze Kui
authors.initials: SK
authors.lastname: Lam
authors.affiliation: Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P. R. China). pchiu@hku.hk.
authors.forename: Pauline
authors.initials: P
authors.lastname: Chiu
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095 (USA). houk@chem.ucla.edu.
authors.forename: Kendall N
authors.initials: KN
authors.lastname: Houk
mesh_terms: D000466:Alkadienes / Q000737:chemistry; D003500:Cyclization; D061565:Cycloaddition Reaction; D003517:Cyclopentanes / Q000737:chemistry; D004852:Epoxy Compounds / Q000737:chemistry*; D008958:Models, Molecular; D012821:Silanes / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000466:Alkadienes; D003517:Cyclopentanes; D004852:Epoxy Compounds; D012821:Silanes
keywords: cycloaddition; density functional calculations; epoxides; reaction mechanisms; stereoselectivity