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 b is-hydrazine 17 gives the bis-hydrazones 1 and 2. These molecular strands a re shown to adopt helical conformations of 1.5 and 2.5 turns, respectively. The helical shape of 1 has been confirmed and structurally characterized b y X-ray crystallography. The results indicate that the pyrimidine-hydrazone unit is a satisfactory helicity codon, so that the facile hydrazone format ion 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 interesti ng routes towards a variety of derived structures.