Enantiodifferentiating photoisomerization of (Z)-cyclooctene and (Z,Z)-cycloocta-1,3-diene sensitized by chiral aromatic amides

Abstract

Optically active benzene(poly)carboxamides with C₂-symmetric pyrrolidine moieties have been employed as chiral sensitizers for the geometrical photoisomerizations of (Z)-cyclooctene (1Z) and (Z,Z)-cycloocta-1,3-diene (1ZZ) in some solvents at varying temperatures. ortho-Substituted di- and tetra-amides used as chiral sensitizers give enantiomeric excesses (ee) up to 14% for both 1Z and 1ZZ in pentane at low temperatures. The use of polar solvents dramatically diminishes the product’s ee, due to the intervention of a free or solvent-separated radical ion pair between 1 and the chiral sensitizer.