A General Approach to Optically Pure (5)-, (6)-, and (7)Heterohelicenes** Jaroslav Z ˇ dny´, Andrej Jancar ˇk, Angelina Andronova, Michal S ˇ mal, Jana Vacek Chocholousov,* Jaroslav Vacek, Radek Pohl, David Saman, Ivana Csarov,