title: Fragment Coupling and the Construction of Quaternary Carbons Using Tertiary Radicals Generated From tert-Alkyl N-Phthalimidoyl Oxalates By Visible-Light Photocatalysis.
abstract: The coupling of tertiary carbon radicals with alkene acceptors is an underdeveloped strategy for uniting complex carbon fragments and forming new quaternary carbons. The scope and limitations of a new approach for generating nucleophilic tertiary radicals from tertiary alcohols and utilizing these intermediates in fragment coupling reactions is described. In this method, the tertiary alcohol is first acylated to give the tert-alkyl N-phthalimidoyl oxalate, which in the presence of visible-light, catalytic Ru(bpy)3(PF6)2, and a reductant fragments to form the corresponding tertiary carbon radical. In addition to reductive coupling with alkenes, substitution reactions of tertiary radicals with allylic and vinylic halides is described. A mechanism for the generation of tertiary carbon radicals from tert-alkyl N-phthalimidoyl oxalates is proposed that is based on earlier pioneering investigations of Okada and Barton. Deuterium labeling and competition experiments reveal that the reductive radical coupling of tert-alkyl N-phthalimidoyl oxalates with electron-deficient alkenes is terminated by hydrogen-atom transfer.
authors.affiliation: Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697-2025.
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Lackner
authors.affiliation: Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697-2025.
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Quasdorf
authors.affiliation: Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697-2025.
authors.forename: Gerald
authors.initials: G
authors.lastname: Pratsch
authors.affiliation: Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697-2025.
authors.forename: Larry E
authors.initials: LE
authors.lastname: Overman
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D005018:Ethyl Chloride / Q000031:analogs & derivatives / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry; D008027:Light; D015394:Molecular Structure; D009861:Onium Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010070:Oxalates / Q000737:chemistry*; D055668:Photochemical Processes; D010797:Phthalimides / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry
chemical_list: C000605691:1-(4-bromo-1H-pyrrol-2-yl)-2,2,2-trichloroethanone; D007093:Imidazoles; D009861:Onium Compounds; D010070:Oxalates; D010797:Phthalimides; D011758:Pyrroles; C000605689:ethyl 4-(4-cyano-1-methyl-1H-imidazol-5-yl)-1-ethyl-1H-pyrrole-2-carboxylate; D005018:Ethyl Chloride; D002244:Carbon