Enforced helicity: efficient access to self-organized helical molecular strands by the imine route

The condensation of the two oligoheterocyclic aldehydes 8 and 16 with the bis-hydrazine 17 gives the bis-hydrazones 1 and 2. These molecular strands are shown to adopt helical conformations of 1.5 and 2.5 turns, respectively. The helical shape of 1 has been confirmed and structurally characterized by X-ray crystallography. The results indicate that the pyrimidine-hydrazone unit is a satisfatory helicity codon, so that the facile hydrazone formation provides an efficient procedure for generating helical structures. This greatly widens the scope of the methodology based on designed heterocyclic sequences for enforcing helicity in molecular strands, and opens interesting routes towards a variety of derived structures.