Enantiopure Chiral Concave 1,10‐Phenanthrolines

Abstract

AbstractChiral information has been introduced into concave 1,10‐phenanthrolines of different ring sizes by using a 2,7‐disubstituted naphthalene bridgehead, which causes axial chirality. A tetraphenolic 2‐(dihydroxynaphthyl)‐9‐(dihydroxyphenyl)‐1,10‐phenanthroline was synthesized as a key intermediate. Two strategies were followed to obtain the bimacrocyclic chiral concave 1,10‐phenanthrolines: quadruple Williamson ether synthesis or alkenylation of the OH groups and subsequent ring‐closing metathesis followed by hydrogenation. The overall yields of bimacrocyles 19 were 10 to 17 % starting from the respective Suzuki coupling of the substituted arenes 11 and 13 to 2,9‐dichloro‐1,10‐phenanthroline (5). Racemic mixtures of the three concave 1,10‐phenanthrolines 19 were separated by using chiral high‐performance liquid chromatography (HPLC) techniques, and their absolute stereochemistry was assigned by comparison of simulated and experimental circular dichroism (CD) spectra. The enantiopure concave 1,10‐phenanthrolines were used as ligands in a copper‐catalysed cyclopropanation, and their selectivity was determined by chiral gas chromatography (GC).