title: How torsional effects cause attack at sterically crowded concave faces of bicyclic alkenes.
abstract: Cycloadditions of 1,3-dipoles and related species to a cis-oxabicyclo[3.3.0]octenone occur on the more sterically crowded concave face. These cycloadditions were studied experimentally by Gais and co-workers in 1998 (Eur. J. Org. Chem. 1998, 257-273) and have now been studied computationally with density functional theory (DFT). Transition states have been computed for various types of (3 + 2) cycloadditions, including diazomethane 1,3-dipolar cycloadditions, a thermally promoted methylenecyclopropane acetal cycloaddition, and a Pd-catalyzed cycloaddition of methylenecyclopropane to an oxabicyclo[3.3.0]octenone. The concave stereoselectivities arise from alkene predistortion that leads to torsional steering in the transition states.
authors: Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095-1569, United States.
authors: Steven A
authors: SA
authors: Lopez
authors: Melika
authors: M
authors: Pourati
authors: Hans-Joachim
authors: HJ
authors: Gais
authors: K N
authors: KN
authors: Houk
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D002384:Catalysis; D061565:Cycloaddition Reaction; D003978:Diazomethane / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D001643:Bridged Bicyclo Compounds; C000599833:oxabicyclo(3.3.0)octenone; D010165:Palladium; D003978:Diazomethane