Synthesis and self-aggregation of cyclic alkynes containing helicene

All stereoisomers of a cyclic alkyne containing three helicene units, 1,12- dimethylbenzo[c]phenanthrene, are synthesized using a building block. Isome ric [3 + 3]cycloalkynes aggregate in organic solvents, Vapor pressure osmom etry reveals dimer formation of (M,M,M)-[3 + 3] cycloalkynes in chloroform and benzene at concentrations above 2 mM. No higher aggregation is observed . The chirality of helicenes plays an important role in self aggregation, a nd diastereomeric (M,P,M)-[3 + 3]cycloalkyne forms a dimer only above 15 mM . Aggregation of racemic (M*,M*,M*)-[3 + 3]cycloalkyne or (M*,P*,M*)-[3 + 3 ]cycloalkyne is much weaker than that of a single enantiomer.