A chiral, bis-anthraquinone-bridged cyclophane with a large specific rotation

A wide variety of common TD-DFT methods predict that chiral cyclophane 1 should exhibit a specific rotation ranging from large ([α]D ∼ 1000) to unreasonably large ([α]D > 1,000,000) with numerous estimates between these values. Compound 1 was prepared in two steps from 1,8-dichloroanthraquinone, and its X-ray structure showed it to be, as expected, a C2-symmetric, roughly triangular macrocycle. Compound 1 was resolved into nearly pure enantiomers by chromatography on a chiral support, and the specific rotations of the two components were determined to be [α]D23 = +1520 and [α]D23 = −1470. These values are large, but not exceptionally so, and the wildly inaccurate TD-DFT estimates of the specific rotation of compound 1 are shown to be closely related to the failure of the same TD-DFT methods to predict accurately the absorption spectrum of 1.

Figure optionsDownload as PowerPoint slide

2,29-Dithiaoctacyclo[28.2.2.17,11.120,24.03,8.010,15.016,21.023,28]hexatriaconta-1(32),3,5,7,10(15),11,13,16(21),17,19,23,25,-27,30,33-pentadecaene-9,22,36,36-tetroneC34H16O4S2[α]D23 = +1520 (c 0.081, CHCl3)Absolute configuration: not determined