Diastereoselective Strategies towards Thia[n]helicenes

In the present study, we have investigated different strategies for diastereoselective synthesis of thian]helicenes. We describe the introduction of different chiral auxiliaries at various positions and investigated their effect in the photocyclization reaction. Different chiral groups were placed at the sterically hindered position of the helical core and their interactions with various solvents and metals like copper were investigated. The use of Cu^I salts has led to high diastereoselectivity in the photocyclization process and we were successful in obtaining the thia5]helicene in enantiomerically pure form in good yield. The single diastereomer obtained was characterized by X‐ray crystallography. From the study of the barrier of racemization of these thia5]helicenes, the stability was found to be comparable to unsubstituted tetrathia7]helicenes and substituted diazadithia7]helicenes. This approach provides an easy access to enantiopure helicenes.