Helically chiral thia- and diselena-quinquephenylophanes

Abstract

Helically chiral thia- and diselena-quinquephenylophanes have been synthesized starting from suitable benzene derivatives via an 8-step synthesis path. Helical thiaquinquephenylophane 9 was obtained from bis(bromomethyl)quinquephenyl 8 in cyclisation with thioacetamide under high-dilution conditions in 10% yield. The corresponding diselenaquinquephenylophane was obtained in 17% yield by using KSeCN and reduction. The M- and P-enantiomers of the thiaphane were separated by HPLC using the Okamoto resin. The CD and UV spectra of the pure M- and P-enantiomers of the thiaphane were recorded. X-Ray structure analyses of the racemic crystals were performed for both compounds. Unit-cell parameters: 9, a= 10.952(1), b= 11.896(2), c= 9.804(1)Å, α= 104.19(1), β= 111.71(1), γ= 80.19(1)°, V= 1146.0(3)ų; 10, a= 10.304(2), b= 15.204(4), c= 9.128(1)Å, α= 105.08(2), β= 113.72(1), γ= 93.41(2)°, V= 1242.2(5)ų. In addition, a dimeric selena-bridged [3.3]quinquephenylophane was observed, and its presence confirmed by FAB-MS and ⁷⁷Se NMR spectroscopy.