Radical aryl migration reactions

Die “Renaissance” der radikalischen Trifluormethylierung

“…[37] Gute Ausbeuten resultierten bei der Umsetzung von Chlor-und Iodbenzol, und es bildeten sich dabei alle drei Isomere mit moderater Selektivität. Die mäßige Regioselektivität ist ein generelles Problem der homolytischen aromatischen Substitution substituierter Arene; [35] Heteroarene zeigen hingegen hçhere Regioselektivitäten bei radikalischen Trifluormethylierungen. Thermische Homolyse von CF 3 I erzeugt das CF 3 CF 3 Br ist deutlich billiger als CF 3 I, allerdings sind wegen der stärkeren C-Br-Bindung die thermische und auch die photochemische C-Br-Homolyse (Initiierung) weniger effizient.…”

Efficient Phenanthrene, Helicene, and Azahelicene Syntheses

“…For example, 1-chloro-and 1-bromophenanthrene were readily prepared from phosphonium salts 5 and 6, respectively, by condensation with 2-iodobenzaldehyde and treatment of the resulting stilbenes 7 and 8 with 2.4 equivalents of tributyltin hydride and 0.4 equivalents of azoisobutyronitrile (AIBN; Scheme 2). [21,22] In each case, the carboniodine bond was homolyzed selectively to generate an aryl radical donor, [19] thus leaving the second halide atom to serve as a protecting group for the attached ortho-carbon atom in the radical acceptor. The same two-step sequence was effective over a broad range of substrates, as evidenced by the examples outlined in Scheme 3 and the Supporting Information.…”

Oxidative Ligand Rearrangement Due to Incipient Aminyl Radicals in the Oxidation of Iron(II) Species with Dioxygen

“…Scheme 3 summarizes downstream steps toward the rearranged ligand (metal has been eliminated for clarity), chief among which is a radical 1,4-(N 1 -to-N 3 ) phenyl migration, [12] which is well documented for carbon atoms and/or heteroatoms. [13] www.eurjic.orgThis study exemplifies a rare case in which a metalbound amido residue, which is vulnerable to one-electron oxidation by dioxygen, can trigger ligand rearrangement by generating an electrophilic aminyl radical that enables a radical 1,4(N-to-N) aryl migration and retention of the radical in a newly formed o-disq -moiety. Similar transformations may be central to other chemical and biological processes that split oxidation equivalents between the metal site and key residues.…”