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Regio-defined amino[5]oxa- and thiahelicenes: a dramatic impact of the nature of the heteroatom on the helical shape and racemization barriers.

The present approach to heterohelicenes provides original [5]oxa- and thiahelicenes, where both oxygen and sulfur atoms are located at the end of the inner helix. Quantum chemical calculations are carried out to determine the pathway for interconversion between two enantiomers and demonstrate that the energy barrier is strongly dependent on the nature of the heteroatom present on the helical shape.