Synthesis of a Chiral Non-Racemic Segmented Screw-Like Oligomer. An Unusual Formof Molecular Chirality

摘要

Described is the synthesis of a chiral non-racemic conjugated organic oligomerthat possesses a linear backbone but has segmented helical functional groups emanating from the backbone. Both antipodes were independently synthesized. The monomer is based upon a chiral non-racemic binaphthalene core with p-bromophenyl groups at the 4 and 4'-positions of the binaphthalene. The monomer was prepared using successive bis(orthometallation) reactions on chiral non-racemic binaphthol. The p-bromophenyl groups were affixed via a Pd(0)-catalyzed cross coupling of 1,4-dibromobenzene and the 4,4'-bis(boronic ester) of the binaphthalene. The final oligomerization was affected by a Ni(0)-promoted coupling of the arylbromides. The new oligomeric framework demonstrates that even highly aligned chiral groups along a common axis are insufficient for large optical rotational enhancements if there is no repeat unit registry.