Memory of Axial Chirality in Aryl Radical Phosphanylations

The rate constant for phosphanylation of an aryl radical with trimethylstannyl diphenylphosphane (Me(3)SnPPh(2)) has been measured as k(phos) approximate to 9 x 10(8) M(-1) s(-1). Aryl radicals derived from several axially chiral o-haloanilides are trapped by Me(3)SnPPh(2) with complete retention of axial chirality as shown by oxidation of the phosphanes to give stable, easily analyzed phosphane oxides or sulfides. Double phosphanylations of o,o'-dihaloanilides followed by treatment with H(2)O(2) or S(8) in either order give enantiomers of a mixed diphosphane oxide sulfide. Chemodivergent trapping of diastereomers of an N-(cyclohex-2-enyl)anilide anilide is observed. For one isomer, the cyclization precedes the Me(3)SnPPh(2) trapping, while for the other isomer direct trapping with Me(3)SnPPh(2) supersedes the cyclization. The products are chiral triaryl phosphanes, oxides, and sulfides that are potentially interesting ligands in asymmetric catalysis.