The Preparation of Enantiopure [6]- and [7]Helicenes from Binaphthanol.

A general and efficient synthetic methodology for the preparation of enantio- and diastereopure [6]-, and [7]helicenes is developed. Commercially available chiral binaphthanols are utilized to generate the arylene-vinylene precursors, which undergo helical folding via photocyclization to give enantio- and diastereopure [6]-, and [7]helicenes. These optically pure helicenes could be easily obtained via silica gel column chromatography without the use of expensive HPLC or chiral resolution reagents. The configurations and structures of these helicenes are confirmed by CD spectra and X-ray crystallographic analysis. This work provides a new method for preparation of enantiopure helicenes.