Organocatalytic hydrogen bond donor/Lewis base (HBD/LB) synthesis and chiroptical properties of thiabridged [5]helicenes.

Thiabridged [5]helicenes are obtained from thioaryl- N -phthalimido benzo[ a ]phenothiazines using a hydrogen bond donor/Lewis base organocatalytic approach. Resolution of [5]helicenes using either (1 S )-(-)-camphanic acid as a chiral auxiliary or CSP-HPLC is reported. Thiabridged [5]helicenes show an exceptional configurational stability with racemization energy barriers higher than 40 kcal mol -1 . Electronic circular dichroism and TD-DFT calculations permit the assignment of the absolute configuration, demonstrating that the sign of optical rotation is not easily related to the M or P structure. Separated enantiomers show circularly polarized luminescence with high dissymmetry ratio.