Pressure and temperature-controlled enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylate mediated by secondary face- and skeleton-modified γ-cyclodextrins

A series of secondary-face-substituted and skeleton-modified γ-cyclodextrins (γ-CDs) were prepared as chiral hosts for enantiodifferentiating [4+4] photocyclodimerization reactions of 2-anthracenecarboxylic acid (AC). These γ-CD derivatives form stable ternary complexes with ACs, with altroside-bearing γ-CDs undergoing induced-fit conformational changes upon complexation, and the photocyclodimerization of AC was, thus, dramatically accelerated. The enantiomeric excess (ee) of anti-head-to-head cyclodimer 3 was greatly enhanced in general with altroside-bearing γ-CDs 7-9. Although mono-altro-γ- CD 9 and 3^A-azido-3^A-deoxy-altro-γ-CD 7 gave 2 in ee's smaller than those obtained with native γ-CD, 3^A-amino- 3^A-deoxy-altro-γ-CD 8 yielded 2 in much higher ee's, which is likely to be ascribed to the combined effects of the less-symmetric cavity and the electrostatic interactions. The influence of temperature and high pressure on the supramolecular photochirogenic reaction has been investigated in depth. An ee as high as 71% was obtained for cyclodimer 2 in the photocyclodimerization of AC mediated by 8 at 210 MPa and -21.5 °C.