Non-Photochemical Route to Chiral Disubstituted [7]Thiaheterohelicenes via Biaryl- and Carbonyl-Coupling Reactions.

Non-photochemical syntheses of optically active dimethyl[7]thiaheterohelicenes (P)-(+)-14 and (M)-(-)-14 are described. The key transformations in the syntheses are the metal-mediated biaryl coupling reactions between two benzodithiophene units having oxazoline moieties and the intramolecular McMurry coupling reaction of the biaryl dialdehydes (S)-13 and (R)-13. The configuration of the atropisomer 10a obtained from the biaryl coupling reaction was shown to be S by X-ray analysis.