Diastereoselective cyclization of an aminobenzoic acid derivative and chiroptical properties of triple-stranded helical bis(phenylethynyl)benzene.

The diastereoselective cyclization of 2,5-dibromo-4-hexylaminobenzoic acid was achieved by the microwave-assisted condensation using SiCl4. Moreover, the triple-stranded helical structure of bis(phenylethynyl)benzene units embedded in the cyclic tri(benzamide) scaffold was obtained by a Sonogashira-Hagihara coupling reaction. Two optically active enantiomers that do not racemize even at the elevated temperature were separated by chiral HPLC. The chiral helical topology was revealed by the spectroscopic data and theoretical calculation.